diff --git a/phpBB/includes/acp/acp_language.php b/phpBB/includes/acp/acp_language.php
index 82a3e570e5..81b14cc02c 100644
--- a/phpBB/includes/acp/acp_language.php
+++ b/phpBB/includes/acp/acp_language.php
@@ -99,7 +99,7 @@ class acp_language
 	/**
 	 * Main handler for acp_language
 	 *
-	 * @param int $id Module ID
+	 * @param string $id Module ID
 	 * @param string $mode Module mode
 	 */
 	public function main($id, $mode)
diff --git a/phpBB/includes/acp/acp_storage.php b/phpBB/includes/acp/acp_storage.php
index 2f651f0e18..adde39baf3 100644
--- a/phpBB/includes/acp/acp_storage.php
+++ b/phpBB/includes/acp/acp_storage.php
@@ -55,7 +55,7 @@ class acp_storage
 	public $u_action;
 
 	/**
-	 *  @param string $id
+	 * @param string $id
 	 * @param string $mode
 	 */
 	public function main($id, $mode)
diff --git a/phpBB/includes/diff/diff.php b/phpBB/includes/diff/diff.php
index bed16285a1..8b7d71020a 100644
--- a/phpBB/includes/diff/diff.php
+++ b/phpBB/includes/diff/diff.php
@@ -340,7 +340,7 @@ class mapped_diff extends diff
 	{
 		if (count($from_lines) != count($mapped_from_lines) || count($to_lines) != count($mapped_to_lines))
 		{
-			return false;
+			return;
 		}
 
 		parent::__construct($mapped_from_lines, $mapped_to_lines);
@@ -760,11 +760,31 @@ class diff3 extends diff
 */
 class diff3_op
 {
+	/**
+	 * @var array|mixed
+	 */
+	protected $orig;
+
+	/**
+	 * @var array|mixed
+	 */
+	protected $final1;
+
+	/**
+	 * @var array|mixed
+	 */
+	protected $final2;
+
+	/**
+	 * @var false
+	 */
+	protected $_merged;
+
 	function __construct($orig = false, $final1 = false, $final2 = false)
 	{
-		$this->orig = $orig ? $orig : array();
-		$this->final1 = $final1 ? $final1 : array();
-		$this->final2 = $final2 ? $final2 : array();
+		$this->orig = $orig ?: array();
+		$this->final1 = $final1 ?: array();
+		$this->final2 = $final2 ?: array();
 	}
 
 	function merged()
@@ -1059,8 +1079,6 @@ class diff3_op
 
 			return;
 		}
-
-		return;
 	}
 }
 
@@ -1074,7 +1092,7 @@ class diff3_op_copy extends diff3_op
 {
 	function __construct($lines = false)
 	{
-		$this->orig = $lines ? $lines : array();
+		$this->orig = $lines ?: array();
 		$this->final1 = &$this->orig;
 		$this->final2 = &$this->orig;
 	}
@@ -1098,6 +1116,21 @@ class diff3_op_copy extends diff3_op
 */
 class diff3_block_builder
 {
+	/**
+	 * @var array
+	 */
+	protected $orig;
+
+	/**
+	 * @var array
+	 */
+	protected $final1;
+
+	/**
+	 * @var array
+	 */
+	protected $final2;
+
 	function __construct()
 	{
 		$this->_init();
diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index 05ea03d446..58c142c740 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -1694,6 +1694,7 @@ function generate_board_url($without_script_path = false)
 * @param string $url The url to redirect to
 * @param bool $return If true, do not redirect but return the sanitized URL. Default is no return.
 * @param bool $disable_cd_check If true, redirect() will redirect to an external domain. If false, the redirect point to the boards url if it does not match the current domain. Default is false.
+* @return string|never
 */
 function redirect($url, $return = false, $disable_cd_check = false)
 {
diff --git a/phpBB/includes/functions_admin.php b/phpBB/includes/functions_admin.php
index 27f9292ac5..54ba46fb67 100644
--- a/phpBB/includes/functions_admin.php
+++ b/phpBB/includes/functions_admin.php
@@ -2487,7 +2487,7 @@ function auto_prune($forum_id, $prune_mode, $prune_flags, $prune_days, $prune_fr
 * @param \phpbb\db\driver\driver_interface $db Database connection
 * @param \phpbb\cache\driver\driver_interface $cache Cache driver
 * @param \phpbb\auth\auth $auth Authentication object
-* @return null
+* @return void
 */
 function phpbb_cache_moderators($db, $cache, $auth)
 {
diff --git a/phpBB/includes/functions_compatibility.php b/phpBB/includes/functions_compatibility.php
index 0783035e6c..dd56aa9622 100644
--- a/phpBB/includes/functions_compatibility.php
+++ b/phpBB/includes/functions_compatibility.php
@@ -122,12 +122,12 @@ function tz_select($default = '', $truncate = false)
 * must be carried through for the moderators table.
 *
 * @deprecated 3.1.0 (To be removed: 4.0.0)
-* @return null
+* @return void
 */
 function cache_moderators()
 {
 	global $db, $cache, $auth;
-	return phpbb_cache_moderators($db, $cache, $auth);
+	phpbb_cache_moderators($db, $cache, $auth);
 }
 
 /**
@@ -249,7 +249,7 @@ function add_log()
  *                              if it changes too frequently (true) to be
  *                              efficiently cached.
  *
- * @return null
+ * @return void
  *
  * @deprecated 3.1.0 (To be removed: 4.0.0)
  */
@@ -279,7 +279,7 @@ function set_config($config_name, $config_value, $is_dynamic = false, \phpbb\con
  *                              if it changes too frequently (true) to be
  *                              efficiently cached.
  *
- * @return null
+ * @return void
  *
  * @deprecated 3.1.0 (To be removed: 4.0.0)
  */
@@ -336,7 +336,7 @@ function request_var($var_name, $default, $multibyte = false, $cookie = false, $
 		$static_request = $request;
 		if (empty($var_name))
 		{
-			return;
+			return null;
 		}
 	}
 	else if ($request === false)
@@ -344,7 +344,7 @@ function request_var($var_name, $default, $multibyte = false, $cookie = false, $
 		$static_request = null;
 		if (empty($var_name))
 		{
-			return;
+			return null;
 		}
 	}
 	$tmp_request = $static_request;
@@ -575,7 +575,7 @@ function upload_attachment($form_name, $forum_id, $local = false, $local_storage
 *						Supported types are: MX (default), A, AAAA, NS, TXT, CNAME
 *						Other types may work or may not work
 *
-* @return mixed		true if entry found,
+* @return bool|null	true if entry found,
 *					false if entry not found,
 *					null if this function is not supported by this environment
 *
@@ -615,7 +615,7 @@ function phpbb_inet_ntop($in_addr)
  *
  * @param string $address	A human readable IPv4 or IPv6 address.
  *
- * @return mixed		false if address is invalid,
+ * @return false|string	false if address is invalid,
  *					in_addr representation of the given address otherwise (string)
  *
  * @deprecated 3.3.0-b2 (To be removed: 4.0.0)
@@ -671,7 +671,7 @@ function phpbb_load_extensions_autoloaders($phpbb_root_path)
 *
 * @param array	$param		Parameter array, see $param_defaults array.
 *
-* @return null
+* @return void
 *
 * @deprecated 3.2.10 (To be removed 4.0.0)
 */
diff --git a/phpBB/includes/functions_content.php b/phpBB/includes/functions_content.php
index 783fa67044..349f3582c4 100644
--- a/phpBB/includes/functions_content.php
+++ b/phpBB/includes/functions_content.php
@@ -144,8 +144,6 @@ function gen_sort_selects(&$limit_days, &$sort_by_text, &$sort_days, &$sort_key,
 		'sorts',
 	);
 	extract($phpbb_dispatcher->trigger_event('core.gen_sort_selects_after', compact($vars)));
-
-	return;
 }
 
 /**
@@ -283,8 +281,6 @@ function make_jumpbox($action, $forum_id = false, $select_all = false, $acl_list
 		'S_JUMPBOX_ACTION'			=> $action,
 		'HIDDEN_FIELDS_FOR_JUMPBOX'	=> build_hidden_fields($url_parts['params']),
 	));
-
-	return;
 }
 
 /**
@@ -441,6 +437,8 @@ function get_context($text, $words, $length = 400)
 	{
 		return str_replace($characters, $entities, ((utf8_strlen($text) >= $length + 3) ? utf8_substr($text, 0, $length) . '...' : $text));
 	}
+
+	return '';
 }
 
 /**
@@ -468,7 +466,7 @@ function phpbb_clean_search_string($search_string)
 *
 * @param string &$message Original message, passed by reference
 * @param string $bbcode_uid BBCode UID
-* @return null
+* @return void
 */
 function decode_message(&$message, $bbcode_uid = '')
 {
@@ -961,7 +959,6 @@ function make_clickable($text, $server_url = false, string $class = 'postlink')
 					if ($value == $static_class)
 					{
 						$element_exists = true;
-						return;
 					}
 				}
 			);
diff --git a/phpBB/includes/functions_display.php b/phpBB/includes/functions_display.php
index 9a1f33db37..e274ae8476 100644
--- a/phpBB/includes/functions_display.php
+++ b/phpBB/includes/functions_display.php
@@ -843,8 +843,6 @@ function generate_forum_nav(&$forum_data_ary)
 	$template->assign_block_vars_array('navlinks', $navlinks_parents);
 	$template->assign_block_vars('navlinks', $navlinks);
 	$template->assign_vars($forum_template_data);
-
-	return;
 }
 
 /**
@@ -966,8 +964,6 @@ function get_moderators(&$forum_moderators, $forum_id = false)
 		}
 	}
 	$db->sql_freeresult($result);
-
-	return;
 }
 
 /**
@@ -999,8 +995,6 @@ function gen_forum_auth_level($mode, $forum_id, $forum_status)
 	{
 		$template->assign_block_vars('rules', array('RULE' => $rule));
 	}
-
-	return;
 }
 
 /**
@@ -1482,8 +1476,6 @@ function watch_topic_forum($mode, &$s_watching, $user_id, $forum_id, $topic_id,
 		$s_watching['title_toggle'] = $user->lang[((!$is_watching) ? 'STOP' : 'START') . '_WATCHING_' . strtoupper($mode)];
 		$s_watching['is_watching'] = $is_watching;
 	}
-
-	return;
 }
 
 /**
diff --git a/phpBB/phpbb/auth/provider/base.php b/phpBB/phpbb/auth/provider/base.php
index 97a8b8d4ad..98945a2ddf 100644
--- a/phpBB/phpbb/auth/provider/base.php
+++ b/phpBB/phpbb/auth/provider/base.php
@@ -79,6 +79,7 @@ abstract class base implements provider_interface
 	*/
 	public function login_link_has_necessary_data(array $login_link_data)
 	{
+		return null;
 	}
 
 	/**
diff --git a/phpBB/phpbb/auth/provider/oauth/oauth.php b/phpBB/phpbb/auth/provider/oauth/oauth.php
index 6925980c94..a9fd2783b6 100644
--- a/phpBB/phpbb/auth/provider/oauth/oauth.php
+++ b/phpBB/phpbb/auth/provider/oauth/oauth.php
@@ -424,6 +424,8 @@ class oauth extends base
 		{
 			return 'LOGIN_LINK_MISSING_DATA';
 		}
+
+		return null;
 	}
 
 	/**
@@ -475,8 +477,6 @@ class oauth extends base
 		// Clear all tokens belonging to the user
 		$storage = new token_storage($this->db, $this->user, $this->oauth_token_table, $this->oauth_state_table);
 		$storage->clearAllTokens();
-
-		return;
 	}
 
 	/**
@@ -617,7 +617,7 @@ class oauth extends base
 	 * @param array		$link_data		The same variable given to
 	 * 									{@see \phpbb\auth\provider\provider_interface::link_account}
 	 * @param string	$service_name	The name of the service being used in linking.
-	 * @return array|string|false		Returns a language constant (string) if an error is encountered,
+	 * @return string|false|never	Returns a language constant (string) if an error is encountered,
 	 * 									an array with error info or false on success.
 	 */
 	protected function link_account_auth_link(array $link_data, $service_name)
@@ -661,7 +661,9 @@ class oauth extends base
 		}
 		else
 		{
-			return $this->set_redirect($service);
+			$this->set_redirect($service);
+
+			return false; // Not reached
 		}
 	}
 
@@ -669,6 +671,7 @@ class oauth extends base
 	 * Performs the query that inserts an account link
 	 *
 	 * @param	array	$data	This array is passed to db->sql_build_array
+	 * @return	void
 	 */
 	protected function link_account_perform_link(array $data)
 	{
@@ -852,6 +855,6 @@ class oauth extends base
 
 		redirect($service->getAuthorizationUri($parameters), false, true);
 
-		return [];
+		return []; // Never reached
 	}
 }
diff --git a/phpBB/phpbb/auth/provider/provider_interface.php b/phpBB/phpbb/auth/provider/provider_interface.php
index 43115892be..7e1f0a7a84 100644
--- a/phpBB/phpbb/auth/provider/provider_interface.php
+++ b/phpBB/phpbb/auth/provider/provider_interface.php
@@ -151,7 +151,7 @@ interface provider_interface
 	*
 	* @param	array	$login_link_data	Any data needed to link a phpBB account to
 	*								an external account.
-	* @return	string|void	Returns a string with a language constant if there
+	* @return	string|null	Returns a string with a language constant if there
 	*						is data missing or void if there is no error.
 	*/
 	public function login_link_has_necessary_data(array $login_link_data);
diff --git a/phpBB/phpbb/avatar/manager.php b/phpBB/phpbb/avatar/manager.php
index 5de3caab10..17fbae09d9 100644
--- a/phpBB/phpbb/avatar/manager.php
+++ b/phpBB/phpbb/avatar/manager.php
@@ -311,7 +311,7 @@ class manager
 	*                               avatar data
 	* @param string         $table Database table from which the avatar should be deleted
 	* @param string         $prefix Prefix of user data columns in database
-	* @return null
+	* @return void
 	*/
 	public function handle_avatar_delete(\phpbb\db\driver\driver_interface $db, \phpbb\user $user, $avatar_data, $table, $prefix)
 	{
diff --git a/phpBB/phpbb/captcha/plugins/qa.php b/phpBB/phpbb/captcha/plugins/qa.php
index 811421a63c..b9bfac33f1 100644
--- a/phpBB/phpbb/captcha/plugins/qa.php
+++ b/phpBB/phpbb/captcha/plugins/qa.php
@@ -1037,7 +1037,8 @@ class qa
 			{
 				return true;
 			}
-			return false;
 		}
+
+		return false;
 	}
 }
diff --git a/phpBB/phpbb/composer/installer.php b/phpBB/phpbb/composer/installer.php
index 354c7ead28..28aaa4171b 100644
--- a/phpBB/phpbb/composer/installer.php
+++ b/phpBB/phpbb/composer/installer.php
@@ -150,6 +150,7 @@ class installer
 	 * @param io\io_interface|null $io IO object used for the output
 	 *
 	 * @throws runtime_exception
+	 * @throws JsonValidationException
 	 */
 	protected function do_install(array $packages, $whitelist, io\io_interface $io = null)
 	{
@@ -501,6 +502,7 @@ class installer
 	 *
 	 * @param array $packages Packages to update.
 	 *        Each entry may be a name or an array associating a version constraint to a name
+	 * @throws JsonValidationException
 	 */
 	protected function generate_ext_json_file(array $packages)
 	{
diff --git a/phpBB/phpbb/config/config.php b/phpBB/phpbb/config/config.php
index c1495a15f0..a63890caf7 100644
--- a/phpBB/phpbb/config/config.php
+++ b/phpBB/phpbb/config/config.php
@@ -106,7 +106,7 @@ class config implements \ArrayAccess, \IteratorAggregate, \Countable
 	* @param  String $key       The configuration option's name
 	* @param  bool   $use_cache Whether this variable should be cached or if it
 	*                           changes too frequently to be efficiently cached
-	* @return null
+	* @return void
 	*/
 	public function delete($key, $use_cache = true)
 	{
diff --git a/phpBB/phpbb/cron/task/core/prune_shadow_topics.php b/phpBB/phpbb/cron/task/core/prune_shadow_topics.php
index 81873a673b..d95f3e500e 100644
--- a/phpBB/phpbb/cron/task/core/prune_shadow_topics.php
+++ b/phpBB/phpbb/cron/task/core/prune_shadow_topics.php
@@ -72,7 +72,7 @@ class prune_shadow_topics extends \phpbb\cron\task\base implements \phpbb\cron\t
 	/**
 	* Runs this cron task.
 	*
-	* @return null
+	* @return void
 	*/
 	public function run()
 	{
@@ -135,7 +135,7 @@ class prune_shadow_topics extends \phpbb\cron\task\base implements \phpbb\cron\t
 	*
 	* @param \phpbb\request\request_interface $request Request object.
 	*
-	* @return null
+	* @return void
 	*/
 	public function parse_parameters(\phpbb\request\request_interface $request)
 	{
diff --git a/phpBB/phpbb/db/driver/driver.php b/phpBB/phpbb/db/driver/driver.php
index b4220d6e6a..c9b4e8db01 100644
--- a/phpBB/phpbb/db/driver/driver.php
+++ b/phpBB/phpbb/db/driver/driver.php
@@ -1246,7 +1246,7 @@ abstract class driver implements driver_interface
 				$this->html_hold .= '<tr>';
 
 				$class = 'row1';
-				foreach (array_values($row) as $val)
+				foreach ($row as $val)
 				{
 					$class = ($class == 'row1') ? 'row2' : 'row1';
 					$this->html_hold .= '<td class="' . $class . '">' . (($val) ? $val : '&nbsp;') . '</td>';
diff --git a/phpBB/phpbb/db/driver/driver_interface.php b/phpBB/phpbb/db/driver/driver_interface.php
index 69a22b3f41..54e3457d3f 100644
--- a/phpBB/phpbb/db/driver/driver_interface.php
+++ b/phpBB/phpbb/db/driver/driver_interface.php
@@ -365,7 +365,7 @@ interface driver_interface
 	*
 	* @param	mixed	$query_id	Already executed query result,
 	*								if false, the last query will be used.
-	* @return	null
+	* @return	void
 	*/
 	public function sql_freeresult($query_id = false);
 
diff --git a/phpBB/phpbb/db/driver/oracle.php b/phpBB/phpbb/db/driver/oracle.php
index b777dcfc72..ee4ad9b5f5 100644
--- a/phpBB/phpbb/db/driver/oracle.php
+++ b/phpBB/phpbb/db/driver/oracle.php
@@ -780,8 +780,6 @@ class oracle extends \phpbb\db\driver\driver
 					$success = @oci_execute($result, OCI_DEFAULT);
 					if ($success)
 					{
-						array();
-
 						while ($row = oci_fetch_array($result, OCI_ASSOC + OCI_RETURN_NULLS))
 						{
 							// Take the time spent on parsing rows into account
diff --git a/phpBB/phpbb/db/extractor/mssql_extractor.php b/phpBB/phpbb/db/extractor/mssql_extractor.php
index 1fa921bc3d..264312a4c4 100644
--- a/phpBB/phpbb/db/extractor/mssql_extractor.php
+++ b/phpBB/phpbb/db/extractor/mssql_extractor.php
@@ -20,7 +20,7 @@ class mssql_extractor extends base_extractor
 	/**
 	* Writes closing line(s) to database backup
 	*
-	* @return null
+	* @return void
 	* @throws extractor_not_initialized_exception when calling this function before init_extractor()
 	*/
 	public function write_end()
@@ -310,7 +310,7 @@ class mssql_extractor extends base_extractor
 	* Extracts data from database table (for ODBC driver)
 	*
 	* @param	string	$table_name	name of the database table
-	* @return null
+	* @return void
 	* @throws extractor_not_initialized_exception when calling this function before init_extractor()
 	*/
 	protected function write_data_odbc($table_name)
diff --git a/phpBB/phpbb/db/extractor/postgres_extractor.php b/phpBB/phpbb/db/extractor/postgres_extractor.php
index 2b271104e8..32267ead4a 100644
--- a/phpBB/phpbb/db/extractor/postgres_extractor.php
+++ b/phpBB/phpbb/db/extractor/postgres_extractor.php
@@ -323,7 +323,7 @@ class postgres_extractor extends base_extractor
 	/**
 	* Writes closing line(s) to database backup
 	*
-	* @return null
+	* @return void
 	* @throws extractor_not_initialized_exception when calling this function before init_extractor()
 	*/
 	public function write_end()
diff --git a/phpBB/phpbb/db/extractor/sqlite3_extractor.php b/phpBB/phpbb/db/extractor/sqlite3_extractor.php
index 92ce9bdcc6..86bb25edde 100644
--- a/phpBB/phpbb/db/extractor/sqlite3_extractor.php
+++ b/phpBB/phpbb/db/extractor/sqlite3_extractor.php
@@ -135,7 +135,7 @@ class sqlite3_extractor extends base_extractor
 	/**
 	* Writes closing line(s) to database backup
 	*
-	* @return null
+	* @return void
 	* @throws extractor_not_initialized_exception when calling this function before init_extractor()
 	*/
 	public function write_end()
diff --git a/phpBB/phpbb/db/migration/tool/config.php b/phpBB/phpbb/db/migration/tool/config.php
index b5404bdba5..77f1d7cfd1 100644
--- a/phpBB/phpbb/db/migration/tool/config.php
+++ b/phpBB/phpbb/db/migration/tool/config.php
@@ -161,5 +161,7 @@ class config implements \phpbb\db\migration\tool\tool_interface
 		{
 			return call_user_func_array(array(&$this, $call), $arguments);
 		}
+
+		return null;
 	}
 }
diff --git a/phpBB/phpbb/db/migration/tool/config_text.php b/phpBB/phpbb/db/migration/tool/config_text.php
index eb3d5b3385..6080619dfa 100644
--- a/phpBB/phpbb/db/migration/tool/config_text.php
+++ b/phpBB/phpbb/db/migration/tool/config_text.php
@@ -126,5 +126,7 @@ class config_text implements \phpbb\db\migration\tool\tool_interface
 		{
 			return call_user_func_array(array(&$this, $call), $arguments);
 		}
+
+		return null;
 	}
 }
diff --git a/phpBB/phpbb/db/migration/tool/module.php b/phpBB/phpbb/db/migration/tool/module.php
index 7c8f80444e..407945e6db 100644
--- a/phpBB/phpbb/db/migration/tool/module.php
+++ b/phpBB/phpbb/db/migration/tool/module.php
@@ -339,7 +339,7 @@ class module implements \phpbb\db\migration\tool\tool_interface
 	* 	Use false to ignore the parent check and check class wide.
 	* @param int|string $module The module id|module_langname
 	* 	specify that here
-	* @return null
+	* @return void
 	* @throws \phpbb\db\migration\exception
 	*/
 	public function remove($class, $parent = 0, $module = '')
@@ -350,7 +350,8 @@ class module implements \phpbb\db\migration\tool\tool_interface
 			if (isset($module['module_langname']))
 			{
 				// Manual Method
-				return $this->remove($class, $parent, $module['module_langname']);
+				$this->remove($class, $parent, $module['module_langname']);
+				return;
 			}
 
 			// Failed.
@@ -443,6 +444,8 @@ class module implements \phpbb\db\migration\tool\tool_interface
 		{
 			return call_user_func_array(array(&$this, $call), $arguments);
 		}
+
+		return null;
 	}
 
 	/**
@@ -470,7 +473,7 @@ class module implements \phpbb\db\migration\tool\tool_interface
 	*	key - module_id
 	*	value - module_langname
 	*
-	* @return null
+	* @return void
 	*/
 	protected function get_categories_list()
 	{
diff --git a/phpBB/phpbb/db/migration/tool/permission.php b/phpBB/phpbb/db/migration/tool/permission.php
index ca070982bf..80d64b403a 100644
--- a/phpBB/phpbb/db/migration/tool/permission.php
+++ b/phpBB/phpbb/db/migration/tool/permission.php
@@ -411,7 +411,7 @@ class permission implements \phpbb\db\migration\tool\tool_interface
 	* @param string $type The type (role|group)
 	* @param bool $has_permission True if you want to give them permission,
 	* 	false if you want to deny them permission
-	* @return null
+	* @return void
 	* @throws \phpbb\db\migration\exception
 	*/
 	public function permission_set($name, $auth_option, $type = 'role', $has_permission = true)
@@ -506,7 +506,8 @@ class permission implements \phpbb\db\migration\tool\tool_interface
 
 					if (count($auth_option))
 					{
-						return $this->permission_set($role_name, $auth_option, 'role', $has_permission);
+						$this->permission_set($role_name, $auth_option, 'role', $has_permission);
+						return;
 					}
 				}
 
@@ -570,7 +571,7 @@ class permission implements \phpbb\db\migration\tool\tool_interface
 	* @param string|array $auth_option The auth_option or array of
 	* 	auth_options you would like to set
 	* @param string $type The type (role|group)
-	* @return null
+	* @return void
 	* @throws \phpbb\db\migration\exception
 	*/
 	public function permission_unset($name, $auth_option, $type = 'role')
@@ -643,7 +644,8 @@ class permission implements \phpbb\db\migration\tool\tool_interface
 						throw new \phpbb\db\migration\exception('ROLE_ASSIGNED_NOT_EXIST', $name, $role_id);
 					}
 
-					return $this->permission_unset($role_name, $auth_option, 'role');
+					$this->permission_unset($role_name, $auth_option, 'role');
+					return;
 				}
 
 				$sql = 'DELETE FROM ' . ACL_GROUPS_TABLE . '
diff --git a/phpBB/phpbb/db/migrator.php b/phpBB/phpbb/db/migrator.php
index 681dfbd735..60673ea9bc 100644
--- a/phpBB/phpbb/db/migrator.php
+++ b/phpBB/phpbb/db/migrator.php
@@ -15,6 +15,7 @@ namespace phpbb\db;
 
 use phpbb\config\config;
 use phpbb\db\driver\driver_interface;
+use phpbb\db\migration\exception;
 use phpbb\db\migration\helper;
 use phpbb\db\output_handler\migrator_output_handler_interface;
 use phpbb\db\output_handler\null_migrator_output_handler;
@@ -157,7 +158,7 @@ class migrator
 	/**
 	* Loads all migrations and their application state from the database.
 	*
-	* @return null
+	* @return void
 	*/
 	public function load_migration_state()
 	{
@@ -203,7 +204,7 @@ class migrator
 	* Sets the list of available migration class names to the given array.
 	*
 	* @param array $class_names An array of migration class names
-	* @return null
+	* @return void
 	*/
 	public function set_migrations($class_names)
 	{
@@ -256,7 +257,7 @@ class migrator
 	* The update step can either be a schema or a (partial) data update. To
 	* check if update() needs to be called again use the finished() method.
 	*
-	* @return null
+	* @return void
 	*/
 	public function update()
 	{
@@ -329,7 +330,7 @@ class migrator
 	*
 	* @param	string	$name The class name of the migration
 	* @return	bool	Whether any update step was successfully run
-	* @throws \phpbb\db\migration\exception
+	* @throws exception
 	*/
 	protected function try_apply($name)
 	{
@@ -365,7 +366,7 @@ class migrator
 			$missing = $this->unfulfillable($depend);
 			if ($missing !== false)
 			{
-				throw new \phpbb\db\migration\exception('MIGRATION_NOT_FULFILLABLE', $name, $missing);
+				throw new exception('MIGRATION_NOT_FULFILLABLE', $name, $missing);
 			}
 
 			if (!isset($this->migration_state[$depend]) ||
@@ -480,7 +481,7 @@ class migrator
 					$this->output_handler->write(array('MIGRATION_DATA_IN_PROGRESS', $name, $elapsed_time), migrator_output_handler_interface::VERBOSITY_VERY_VERBOSE);
 				}
 			}
-			catch (\phpbb\db\migration\exception $e)
+			catch (exception $e)
 			{
 				// Reset data state and revert the schema changes
 				$state['migration_data_state'] = '';
@@ -653,7 +654,7 @@ class migrator
 	* @param bool $revert true to revert a data step
 	* @return bool|array migration state. True if completed, serialized array if not finished
 	* @psalm-return bool|array{result: mixed, step: int}
-	* @throws \phpbb\db\migration\exception
+	* @throws exception
 	*/
 	protected function process_data_step($steps, $state, $revert = false)
 	{
@@ -693,7 +694,7 @@ class migrator
 				);
 			}
 		}
-		catch (\phpbb\db\migration\exception $e)
+		catch (exception $e)
 		{
 			// We should try rolling back here
 			foreach ($steps as $reverse_step_identifier => $reverse_step)
@@ -715,15 +716,16 @@ class migrator
 	}
 
 	/**
-	* Run a single step
-	*
-	* An exception should be thrown if an error occurs
-	*
-	* @param mixed $step Data step from migration
-	* @param mixed $last_result Result to pass to the callable (only for 'custom' method)
-	* @param bool $reverse False to install, True to attempt uninstallation by reversing the call
-	* @return null
-	*/
+	 * Run a single step
+	 *
+	 * An exception should be thrown if an error occurs
+	 *
+	 * @param mixed $step Data step from migration
+	 * @param mixed $last_result Result to pass to the callable (only for 'custom' method)
+	 * @param bool $reverse False to install, True to attempt uninstallation by reversing the call
+	 * @return mixed
+	 * @throws exception
+	 */
 	protected function run_step($step, $last_result = 0, $reverse = false)
 	{
 		$callable_and_parameters = $this->get_callable_from_step($step, $last_result, $reverse);
@@ -747,7 +749,7 @@ class migrator
 	* @param bool $reverse False to install, True to attempt uninstallation by reversing the call
 	* @return array|false Array with parameters for call_user_func_array(), 0 is the callable, 1 is parameters;
 	*					false if no callable can be created from data setp
-	* @throws \phpbb\db\migration\exception
+	* @throws exception
 	*/
 	protected function get_callable_from_step(array $step, $last_result = 0, $reverse = false)
 	{
@@ -769,12 +771,12 @@ class migrator
 			case 'if':
 				if (!isset($parameters[0]))
 				{
-					throw new \phpbb\db\migration\exception('MIGRATION_INVALID_DATA_MISSING_CONDITION', $step);
+					throw new exception('MIGRATION_INVALID_DATA_MISSING_CONDITION', $step);
 				}
 
 				if (!isset($parameters[1]))
 				{
-					throw new \phpbb\db\migration\exception('MIGRATION_INVALID_DATA_MISSING_STEP', $step);
+					throw new exception('MIGRATION_INVALID_DATA_MISSING_STEP', $step);
 				}
 
 				if ($reverse)
@@ -799,7 +801,7 @@ class migrator
 			case 'custom':
 				if (!is_callable($parameters[0]))
 				{
-					throw new \phpbb\db\migration\exception('MIGRATION_INVALID_DATA_CUSTOM_NOT_CALLABLE', $step);
+					throw new exception('MIGRATION_INVALID_DATA_CUSTOM_NOT_CALLABLE', $step);
 				}
 
 				if ($reverse)
@@ -818,17 +820,17 @@ class migrator
 			default:
 				if (!$method)
 				{
-					throw new \phpbb\db\migration\exception('MIGRATION_INVALID_DATA_UNKNOWN_TYPE', $step);
+					throw new exception('MIGRATION_INVALID_DATA_UNKNOWN_TYPE', $step);
 				}
 
 				if (!isset($this->tools[$class]))
 				{
-					throw new \phpbb\db\migration\exception('MIGRATION_INVALID_DATA_UNDEFINED_TOOL', $step);
+					throw new exception('MIGRATION_INVALID_DATA_UNDEFINED_TOOL', $step);
 				}
 
 				if (!method_exists(get_class($this->tools[$class]), $method))
 				{
-					throw new \phpbb\db\migration\exception('MIGRATION_INVALID_DATA_UNDEFINED_METHOD', $step);
+					throw new exception('MIGRATION_INVALID_DATA_UNDEFINED_METHOD', $step);
 				}
 
 				// Attempt to reverse operations
@@ -855,7 +857,7 @@ class migrator
 	*
 	* @param string $name Name of the migration
 	* @param array $state
-	* @return null
+	* @return void
 	*/
 	protected function set_migration_state($name, $state)
 	{
@@ -993,7 +995,7 @@ class migrator
 	* THIS WILL THROW ERRORS IF MIGRATIONS ALREADY EXIST IN THE TABLE, DO NOT CALL MORE THAN ONCE!
 	*
 	* @param array $migrations Array of migrations (names) to add to the migrations table
-	* @return null
+	* @return void
 	*/
 	public function populate_migrations($migrations)
 	{
@@ -1016,7 +1018,7 @@ class migrator
 
 	/**
 	* Creates the migrations table if it does not exist.
-	* @return null
+	* @return void
 	*/
 	public function create_migrations_table()
 	{
diff --git a/phpBB/phpbb/di/container_builder.php b/phpBB/phpbb/di/container_builder.php
index b9dc8bba63..33852ba08c 100644
--- a/phpBB/phpbb/di/container_builder.php
+++ b/phpBB/phpbb/di/container_builder.php
@@ -143,6 +143,7 @@ class container_builder
 	 * Build and return a new Container respecting the current configuration
 	 *
 	 * @return \phpbb_cache_container|ContainerBuilder
+	 * @throws \Exception
 	 */
 	public function get_container()
 	{
diff --git a/phpBB/phpbb/event/md_exporter.php b/phpBB/phpbb/event/md_exporter.php
index 84e04133de..fcc5b78afc 100644
--- a/phpBB/phpbb/event/md_exporter.php
+++ b/phpBB/phpbb/event/md_exporter.php
@@ -429,7 +429,7 @@ class md_exporter
 	* Validates a template event name
 	*
 	* @param $event_name
-	* @return null
+	* @return void
 	* @throws \LogicException
 	*/
 	public function validate_event_name($event_name)
diff --git a/phpBB/phpbb/event/php_exporter.php b/phpBB/phpbb/event/php_exporter.php
index ba8ffbbe36..2dfb877fa6 100644
--- a/phpBB/phpbb/event/php_exporter.php
+++ b/phpBB/phpbb/event/php_exporter.php
@@ -84,7 +84,7 @@ class php_exporter
 	*
 	* @param string	$name	Name of the current event (used for error messages)
 	* @param int	$line	Line where the current event is placed in
-	* @return null
+	* @return void
 	*/
 	public function set_current_event($name, $line)
 	{
@@ -96,7 +96,7 @@ class php_exporter
 	* Set the content of this file
 	*
 	* @param array $content		Array with the lines of the file
-	* @return null
+	* @return void
 	*/
 	public function set_content($content)
 	{
@@ -790,7 +790,7 @@ class php_exporter
 	*
 	* @param array $vars_array		Variables found in the array line
 	* @param array $vars_docblock	Variables found in the doc block
-	* @return null
+	* @return void
 	* @throws \LogicException
 	*/
 	public function validate_vars_docblock_array($vars_array, $vars_docblock)
diff --git a/phpBB/phpbb/extension/manager.php b/phpBB/phpbb/extension/manager.php
index 27257239f6..24dfeb75b4 100644
--- a/phpBB/phpbb/extension/manager.php
+++ b/phpBB/phpbb/extension/manager.php
@@ -254,7 +254,7 @@ class manager
 	* so never call this in a script that has a max_execution time.
 	*
 	* @param string $name The extension's name
-	* @return null
+	* @return void
 	*/
 	public function enable($name)
 	{
@@ -302,7 +302,7 @@ class manager
 	* while so never call this in a script that has a max_execution time.
 	*
 	* @param string $name The extension's name
-	* @return null
+	* @return void
 	*/
 	public function disable($name)
 	{
@@ -357,7 +357,7 @@ class manager
 	* so never call this in a script that has a max_execution time.
 	*
 	* @param string $name The extension's name
-	* @return null
+	* @return void
 	*/
 	public function purge($name)
 	{
diff --git a/phpBB/phpbb/file_downloader.php b/phpBB/phpbb/file_downloader.php
index 75721b0f05..873bccc9e8 100644
--- a/phpBB/phpbb/file_downloader.php
+++ b/phpBB/phpbb/file_downloader.php
@@ -30,7 +30,7 @@ class file_downloader
 	 * @param int		$port			Port to connect to; default: 80
 	 * @param int		$timeout		Connection timeout in seconds; default: 6
 	 *
-	 * @return mixed File data as string if file can be read and there is no
+	 * @return false|string File data as string if file can be read and there is no
 	 *			timeout, false if there were errors or the connection timed out
 	 *
 	 * @throws \phpbb\exception\runtime_exception If data can't be retrieved and no error
diff --git a/phpBB/phpbb/groupposition/legend.php b/phpBB/phpbb/groupposition/legend.php
index fb4ea44af6..fd20896473 100644
--- a/phpBB/phpbb/groupposition/legend.php
+++ b/phpBB/phpbb/groupposition/legend.php
@@ -110,12 +110,13 @@ class legend implements \phpbb\groupposition\groupposition_interface
 	}
 
 	/**
-	* Deletes a group by setting the field to self::GROUP_DISABLED and closing the gap in the list.
-	*
-	* @param	int		$group_id		group_id of the group to be deleted
-	* @param	bool	$skip_group		Skip setting the value for this group, to save the query, when you need to update it anyway.
-	* @return	bool		True if the group was deleted successfully
-	*/
+	 * Deletes a group by setting the field to self::GROUP_DISABLED and closing the gap in the list.
+	 *
+	 * @param int $group_id group_id of the group to be deleted
+	 * @param bool $skip_group Skip setting the value for this group, to save the query, when you need to update it anyway.
+	 * @return    bool        True if the group was deleted successfully
+	 * @throws exception
+	 */
 	public function delete_group($group_id, $skip_group = false)
 	{
 		$current_value = $this->get_group_value($group_id);
diff --git a/phpBB/phpbb/install/console/command/install/config/show.php b/phpBB/phpbb/install/console/command/install/config/show.php
index 7daede1b04..138f74e74f 100644
--- a/phpBB/phpbb/install/console/command/install/config/show.php
+++ b/phpBB/phpbb/install/console/command/install/config/show.php
@@ -96,7 +96,7 @@ class show extends \phpbb\console\command\command
 
 		try
 		{
-			$config = Yaml::parse(file_get_contents($config_file), true, false);
+			$config = Yaml::parse(file_get_contents($config_file), true);
 		}
 		catch (ParseException $e)
 		{
@@ -119,7 +119,7 @@ class show extends \phpbb\console\command\command
 			return Command::FAILURE;
 		}
 
-		$style->block(Yaml::dump(array('installer' => $config), 10, 4, true, false));
+		$style->block(Yaml::dump(array('installer' => $config), 10, 4, true));
 
 		return Command::SUCCESS;
 	}
diff --git a/phpBB/phpbb/install/console/command/install/config/validate.php b/phpBB/phpbb/install/console/command/install/config/validate.php
index eb638ad387..2682756c13 100644
--- a/phpBB/phpbb/install/console/command/install/config/validate.php
+++ b/phpBB/phpbb/install/console/command/install/config/validate.php
@@ -96,7 +96,7 @@ class validate extends \phpbb\console\command\command
 
 		try
 		{
-			$config = Yaml::parse(file_get_contents($config_file), true, false);
+			$config = Yaml::parse(file_get_contents($config_file), true);
 		}
 		catch (ParseException $e)
 		{
diff --git a/phpBB/phpbb/install/console/command/install/install.php b/phpBB/phpbb/install/console/command/install/install.php
index 1ad4ea8114..84c8aa688a 100644
--- a/phpBB/phpbb/install/console/command/install/install.php
+++ b/phpBB/phpbb/install/console/command/install/install.php
@@ -16,6 +16,7 @@ namespace phpbb\install\console\command\install;
 use phpbb\install\exception\installer_exception;
 use phpbb\install\helper\install_helper;
 use phpbb\install\helper\iohandler\cli_iohandler;
+use phpbb\install\helper\iohandler\exception\iohandler_not_implemented_exception;
 use phpbb\install\helper\iohandler\factory;
 use phpbb\install\installer;
 use phpbb\install\installer_configuration;
@@ -90,10 +91,11 @@ class install extends \phpbb\console\command\command
 	 *
 	 * Install the board
 	 *
-	 * @param InputInterface  $input  An InputInterface instance
+	 * @param InputInterface $input An InputInterface instance
 	 * @param OutputInterface $output An OutputInterface instance
 	 *
 	 * @return int 0 if everything went fine, or a non-zero exit code
+	 * @throws iohandler_not_implemented_exception
 	 */
 	protected function execute(InputInterface $input, OutputInterface $output)
 	{
@@ -124,7 +126,7 @@ class install extends \phpbb\console\command\command
 
 		try
 		{
-			$config = Yaml::parse(file_get_contents($config_file), true, false);
+			$config = Yaml::parse(file_get_contents($config_file), true);
 		}
 		catch (ParseException $e)
 		{
diff --git a/phpBB/phpbb/install/console/command/update/config/show.php b/phpBB/phpbb/install/console/command/update/config/show.php
index df7a69ed31..85f90e14aa 100644
--- a/phpBB/phpbb/install/console/command/update/config/show.php
+++ b/phpBB/phpbb/install/console/command/update/config/show.php
@@ -96,7 +96,7 @@ class show extends \phpbb\console\command\command
 
 		try
 		{
-			$config = Yaml::parse(file_get_contents($config_file), true, false);
+			$config = Yaml::parse(file_get_contents($config_file), true);
 		}
 		catch (ParseException $e)
 		{
@@ -119,7 +119,7 @@ class show extends \phpbb\console\command\command
 			return Command::FAILURE;
 		}
 
-		$style->block(Yaml::dump(array('updater' => $config), 10, 4, true, false));
+		$style->block(Yaml::dump(array('updater' => $config), 10, 4, true));
 
 		return Command::SUCCESS;
 	}
diff --git a/phpBB/phpbb/install/console/command/update/config/validate.php b/phpBB/phpbb/install/console/command/update/config/validate.php
index eb1a48546f..69fba0f7a8 100644
--- a/phpBB/phpbb/install/console/command/update/config/validate.php
+++ b/phpBB/phpbb/install/console/command/update/config/validate.php
@@ -96,7 +96,7 @@ class validate extends \phpbb\console\command\command
 
 		try
 		{
-			$config = Yaml::parse(file_get_contents($config_file), true, false);
+			$config = Yaml::parse(file_get_contents($config_file), true);
 		}
 		catch (ParseException $e)
 		{
diff --git a/phpBB/phpbb/install/console/command/update/update.php b/phpBB/phpbb/install/console/command/update/update.php
index f3320d358b..3c70231c20 100644
--- a/phpBB/phpbb/install/console/command/update/update.php
+++ b/phpBB/phpbb/install/console/command/update/update.php
@@ -124,7 +124,7 @@ class update extends \phpbb\console\command\command
 
 		try
 		{
-			$config = Yaml::parse(file_get_contents($config_file), true, false);
+			$config = Yaml::parse(file_get_contents($config_file), true);
 		}
 		catch (ParseException $e)
 		{
diff --git a/phpBB/phpbb/install/controller/install.php b/phpBB/phpbb/install/controller/install.php
index 47acc2953f..df6da1e3db 100644
--- a/phpBB/phpbb/install/controller/install.php
+++ b/phpBB/phpbb/install/controller/install.php
@@ -99,6 +99,7 @@ class install
 	 * @return Response|StreamedResponse
 	 *
 	 * @throws http_exception When phpBB is already installed
+	 * @throws \phpbb\install\helper\iohandler\exception\iohandler_not_implemented_exception
 	 * @psalm-suppress InvalidNullableReturnType
 	 */
 	public function handle()
diff --git a/phpBB/phpbb/install/helper/iohandler/ajax_iohandler.php b/phpBB/phpbb/install/helper/iohandler/ajax_iohandler.php
index b150d7098e..62ef42108d 100644
--- a/phpBB/phpbb/install/helper/iohandler/ajax_iohandler.php
+++ b/phpBB/phpbb/install/helper/iohandler/ajax_iohandler.php
@@ -94,9 +94,9 @@ class ajax_iohandler extends iohandler_base
 	 * @param \phpbb\request\request_interface	$request	HTTP request interface
 	 * @param \phpbb\template\template			$template	Template engine
 	 * @param router 							$router		Router
-	 * @param string 							$root_path	Path to phpBB's root
+	 * @param string $root_path	Path to phpBB's root
 	 */
-	public function __construct(path_helper $path_helper, \phpbb\request\request_interface $request, \phpbb\template\template $template, router $router, $root_path)
+	public function __construct(path_helper $path_helper, \phpbb\request\request_interface $request, \phpbb\template\template $template, router $router, string $root_path)
 	{
 		$this->path_helper = $path_helper;
 		$this->request	= $request;
diff --git a/phpBB/phpbb/log/log.php b/phpBB/phpbb/log/log.php
index 385251eaab..054e8bdda8 100644
--- a/phpBB/phpbb/log/log.php
+++ b/phpBB/phpbb/log/log.php
@@ -129,7 +129,7 @@ class log implements \phpbb\log\log_interface
 	* in get_logs()
 	*
 	* @param	bool	$is_in_admin		Are we called from within the acp?
-	* @return	null
+	* @return	void
 	*/
 	public function set_is_admin($is_in_admin)
 	{
@@ -150,7 +150,7 @@ class log implements \phpbb\log\log_interface
 	* Set table name
 	*
 	* @param	string	$log_table		Can overwrite the table to use for the logs
-	* @return	null
+	* @return	void
 	*/
 	public function set_log_table($log_table)
 	{
diff --git a/phpBB/phpbb/message/message.php b/phpBB/phpbb/message/message.php
index 53821d5412..d77f56c73f 100644
--- a/phpBB/phpbb/message/message.php
+++ b/phpBB/phpbb/message/message.php
@@ -65,7 +65,7 @@ class message
 	* Set the subject of the email
 	*
 	* @param string $subject
-	* @return null
+	* @return void
 	*/
 	public function set_subject($subject)
 	{
@@ -76,7 +76,7 @@ class message
 	* Set the body of the email text
 	*
 	* @param string $body
-	* @return null
+	* @return void
 	*/
 	public function set_body($body)
 	{
@@ -87,7 +87,7 @@ class message
 	* Set the name of the email template to use
 	*
 	* @param string $template
-	* @return null
+	* @return void
 	*/
 	public function set_template($template)
 	{
@@ -98,7 +98,7 @@ class message
 	* Set the array with the "template" data for the email
 	*
 	* @param array $template_vars
-	* @return null
+	* @return void
 	*/
 	public function set_template_vars($template_vars)
 	{
@@ -109,7 +109,7 @@ class message
 	* Add a recipient from \phpbb\user
 	*
 	* @param array $user
-	* @return null
+	* @return void
 	*/
 	public function add_recipient_from_user_row(array $user)
 	{
@@ -132,7 +132,7 @@ class message
 	* @param int $recipient_notify_type	Used notification methods (Jabber, Email, ...)
 	* @param string $recipient_username	User Name (used for AntiAbuse header)
 	* @param string $recipient_jabber
-	* @return null
+	* @return void
 	*/
 	public function add_recipient($recipient_name, $recipient_address, $recipient_lang, $recipient_notify_type = NOTIFY_EMAIL, $recipient_username = '', $recipient_jabber = '')
 	{
@@ -151,7 +151,7 @@ class message
 	* Set the senders data from \phpbb\user object
 	*
 	* @param \phpbb\user $user
-	* @return null
+	* @return void
 	*/
 	public function set_sender_from_user($user)
 	{
@@ -178,7 +178,7 @@ class message
 	* @param int $sender_id				User ID
 	* @param string $sender_username	User Name (used for AntiAbuse header)
 	* @param string $sender_jabber
-	* @return null
+	* @return void
 	*/
 	public function set_sender($sender_ip, $sender_name, $sender_address, $sender_lang = '', $sender_id = 0, $sender_username = '', $sender_jabber = '')
 	{
@@ -195,7 +195,7 @@ class message
 	* Which notification type should be used? Jabber, Email, ...?
 	*
 	* @param int $sender_notify_type
-	* @return null
+	* @return void
 	*/
 	public function set_sender_notify_type($sender_notify_type)
 	{
@@ -205,7 +205,7 @@ class message
 	/**
 	* Ok, now the same email if CC specified, but without exposing the user's email address
 	*
-	* @return null
+	* @return void
 	*/
 	public function cc_sender()
 	{
diff --git a/phpBB/phpbb/notification/method/email.php b/phpBB/phpbb/notification/method/email.php
index ce81c58185..cffd259c0e 100644
--- a/phpBB/phpbb/notification/method/email.php
+++ b/phpBB/phpbb/notification/method/email.php
@@ -117,7 +117,7 @@ class email extends \phpbb\notification\method\messenger_base
 
 		$insert_buffer->flush();
 
-		return $this->notify_using_messenger(NOTIFY_EMAIL);
+		$this->notify_using_messenger(NOTIFY_EMAIL);
 	}
 
 	/**
diff --git a/phpBB/phpbb/notification/type/admin_activate_user.php b/phpBB/phpbb/notification/type/admin_activate_user.php
index 1d8d5717f4..99a758c116 100644
--- a/phpBB/phpbb/notification/type/admin_activate_user.php
+++ b/phpBB/phpbb/notification/type/admin_activate_user.php
@@ -29,8 +29,10 @@ class admin_activate_user extends \phpbb\notification\type\base
 	}
 
 	/**
-	* {@inheritdoc}
-	*/
+	 * Language key used to output the text
+	 *
+	 * @var string
+	 */
 	protected $language_key = 'NOTIFICATION_ADMIN_ACTIVATE_USER';
 
 	/**
diff --git a/phpBB/phpbb/notification/type/approve_post.php b/phpBB/phpbb/notification/type/approve_post.php
index 98b04cc7cc..7c242b75da 100644
--- a/phpBB/phpbb/notification/type/approve_post.php
+++ b/phpBB/phpbb/notification/type/approve_post.php
@@ -128,9 +128,7 @@ class approve_post extends \phpbb\notification\type\post
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/approve_topic.php b/phpBB/phpbb/notification/type/approve_topic.php
index d072ff330a..c28d94e3f5 100644
--- a/phpBB/phpbb/notification/type/approve_topic.php
+++ b/phpBB/phpbb/notification/type/approve_topic.php
@@ -127,9 +127,7 @@ class approve_topic extends \phpbb\notification\type\topic
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/base.php b/phpBB/phpbb/notification/type/base.php
index 7c77154fe7..54a9319d26 100644
--- a/phpBB/phpbb/notification/type/base.php
+++ b/phpBB/phpbb/notification/type/base.php
@@ -129,7 +129,7 @@ abstract class base implements \phpbb\notification\type\type_interface
 	*/
 	public function __get($name)
 	{
-		return (!isset($this->data[$name])) ? null : $this->data[$name];
+		return $this->data[$name] ?? null;
 	}
 
 
@@ -139,13 +139,24 @@ abstract class base implements \phpbb\notification\type\type_interface
 	* @param mixed $name
 	* @param mixed $value
 	*
-	* @return null
+	* @return void
 	*/
 	public function __set($name, $value)
 	{
 		$this->data[$name] = $value;
 	}
 
+	/**
+	 * Magic method check if a variable is defined and is not null
+	 *
+	 * @param mixed $name
+	 *
+	 * @return bool
+	 */
+	public function __isset($name)
+	{
+		return isset($this->data[$name]);
+	}
 
 	/**
 	* Magic method to get a string of this notification
@@ -394,7 +405,6 @@ abstract class base implements \phpbb\notification\type\type_interface
 	 */
 	public function load_special($data, $notifications)
 	{
-		return;
 	}
 
 	/**
@@ -407,6 +417,14 @@ abstract class base implements \phpbb\notification\type\type_interface
 		return true;
 	}
 
+	/**
+	 * {@inheritdoc}
+	 */
+	public function get_email_template()
+	{
+		return false;
+	}
+
 	/**
 	 * Pre create insert array function (fall back)
 	 *
diff --git a/phpBB/phpbb/notification/type/bookmark.php b/phpBB/phpbb/notification/type/bookmark.php
index 487e3a7543..98a759c300 100644
--- a/phpBB/phpbb/notification/type/bookmark.php
+++ b/phpBB/phpbb/notification/type/bookmark.php
@@ -57,13 +57,14 @@ class bookmark extends \phpbb\notification\type\post
 	}
 
 	/**
-	* Find the users who want to receive notifications
-	*
-	* @param array $type_data Data from submit_post
-	* @param array $options Options for finding users for notification
-	*
-	* @return array
-	*/
+	 * Find the users who want to receive notifications
+	 *
+	 * @param array $type_data Data from submit_post
+	 * @param array $options Options for finding users for notification
+	 *
+	 * @return array
+	 * @throws \Exception
+	 */
 	public function find_users_for_notification($type_data, $options = array())
 	{
 		$options = array_merge(array(
@@ -117,9 +118,7 @@ class bookmark extends \phpbb\notification\type\post
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/disapprove_post.php b/phpBB/phpbb/notification/type/disapprove_post.php
index a92a69cf03..b7805dd0ec 100644
--- a/phpBB/phpbb/notification/type/disapprove_post.php
+++ b/phpBB/phpbb/notification/type/disapprove_post.php
@@ -148,9 +148,7 @@ class disapprove_post extends \phpbb\notification\type\approve_post
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/disapprove_topic.php b/phpBB/phpbb/notification/type/disapprove_topic.php
index d5e9b64804..5b9d03d238 100644
--- a/phpBB/phpbb/notification/type/disapprove_topic.php
+++ b/phpBB/phpbb/notification/type/disapprove_topic.php
@@ -148,9 +148,7 @@ class disapprove_topic extends \phpbb\notification\type\approve_topic
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/forum.php b/phpBB/phpbb/notification/type/forum.php
index 2d196f013f..181316e922 100644
--- a/phpBB/phpbb/notification/type/forum.php
+++ b/phpBB/phpbb/notification/type/forum.php
@@ -104,9 +104,7 @@ class forum extends \phpbb\notification\type\post
 	}
 
 	/**
-	 * Get email template
-	 *
-	 * @return string|bool
+	 * {@inheritdoc}
 	 */
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/pm.php b/phpBB/phpbb/notification/type/pm.php
index 8dffbc1bf4..276d1984fb 100644
--- a/phpBB/phpbb/notification/type/pm.php
+++ b/phpBB/phpbb/notification/type/pm.php
@@ -145,9 +145,7 @@ class pm extends \phpbb\notification\type\base
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/post.php b/phpBB/phpbb/notification/type/post.php
index 022e184110..be8c8d75e9 100644
--- a/phpBB/phpbb/notification/type/post.php
+++ b/phpBB/phpbb/notification/type/post.php
@@ -238,9 +238,7 @@ class post extends \phpbb\notification\type\base
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/post_in_queue.php b/phpBB/phpbb/notification/type/post_in_queue.php
index a02dd9684e..3d818a1b27 100644
--- a/phpBB/phpbb/notification/type/post_in_queue.php
+++ b/phpBB/phpbb/notification/type/post_in_queue.php
@@ -152,9 +152,7 @@ class post_in_queue extends \phpbb\notification\type\post
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/quote.php b/phpBB/phpbb/notification/type/quote.php
index f8fd8e4d81..98224917e9 100644
--- a/phpBB/phpbb/notification/type/quote.php
+++ b/phpBB/phpbb/notification/type/quote.php
@@ -149,9 +149,7 @@ class quote extends \phpbb\notification\type\post
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/report_pm.php b/phpBB/phpbb/notification/type/report_pm.php
index c8a1ccae69..f542eccf20 100644
--- a/phpBB/phpbb/notification/type/report_pm.php
+++ b/phpBB/phpbb/notification/type/report_pm.php
@@ -125,9 +125,7 @@ class report_pm extends \phpbb\notification\type\pm
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/report_pm_closed.php b/phpBB/phpbb/notification/type/report_pm_closed.php
index 083baeece8..06186a868c 100644
--- a/phpBB/phpbb/notification/type/report_pm_closed.php
+++ b/phpBB/phpbb/notification/type/report_pm_closed.php
@@ -84,9 +84,7 @@ class report_pm_closed extends \phpbb\notification\type\pm
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/report_post.php b/phpBB/phpbb/notification/type/report_post.php
index 730a6a12f4..1aeac139eb 100644
--- a/phpBB/phpbb/notification/type/report_post.php
+++ b/phpBB/phpbb/notification/type/report_post.php
@@ -91,9 +91,7 @@ class report_post extends \phpbb\notification\type\post_in_queue
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/report_post_closed.php b/phpBB/phpbb/notification/type/report_post_closed.php
index 9e05e4c9cd..e71901a61c 100644
--- a/phpBB/phpbb/notification/type/report_post_closed.php
+++ b/phpBB/phpbb/notification/type/report_post_closed.php
@@ -91,9 +91,7 @@ class report_post_closed extends \phpbb\notification\type\post
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/topic.php b/phpBB/phpbb/notification/type/topic.php
index 715e0d47ed..7ecb5e6e85 100644
--- a/phpBB/phpbb/notification/type/topic.php
+++ b/phpBB/phpbb/notification/type/topic.php
@@ -191,9 +191,7 @@ class topic extends \phpbb\notification\type\base
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/notification/type/topic_in_queue.php b/phpBB/phpbb/notification/type/topic_in_queue.php
index 523b8eb5a3..bfdec5278b 100644
--- a/phpBB/phpbb/notification/type/topic_in_queue.php
+++ b/phpBB/phpbb/notification/type/topic_in_queue.php
@@ -144,9 +144,7 @@ class topic_in_queue extends \phpbb\notification\type\topic
 	}
 
 	/**
-	* Get email template
-	*
-	* @return string|bool
+	* {@inheritdoc}
 	*/
 	public function get_email_template()
 	{
diff --git a/phpBB/phpbb/plupload/plupload.php b/phpBB/phpbb/plupload/plupload.php
index ed749fdbe0..aeb1bd87d2 100644
--- a/phpBB/phpbb/plupload/plupload.php
+++ b/phpBB/phpbb/plupload/plupload.php
@@ -100,7 +100,7 @@ class plupload
 		// and handle the file as usual
 		if ($chunks_expected < 2)
 		{
-			return;
+			return null;
 		}
 
 		$file_name = $this->request->variable('name', '');
@@ -150,7 +150,7 @@ class plupload
 	* @param int						$forum_id The ID of the forum
 	* @param int						$max_files Maximum number of files allowed. 0 for unlimited.
 	*
-	* @return null
+	* @return void
 	*/
 	public function configure(\phpbb\cache\service $cache, \phpbb\template\template $template, $s_action, $forum_id, $max_files)
 	{
@@ -200,7 +200,7 @@ class plupload
 	* @param int $code		The error code
 	* @param string $msg	The translation string of the message to be sent
 	*
-	* @return null
+	* @return void
 	*/
 	public function emit_error($code, $msg)
 	{
@@ -331,7 +331,7 @@ class plupload
 	* @param int $chunk Chunk number
 	* @param string $file_path File path
 	*
-	* @return null
+	* @return void
 	*/
 	protected function integrate_uploaded_file($form_name, $chunk, $file_path)
 	{
@@ -378,7 +378,7 @@ class plupload
 	/**
 	* Creates the temporary directory if it does not already exist.
 	*
-	* @return null
+	* @return void
 	*/
 	protected function prepare_temporary_directory()
 	{
@@ -396,7 +396,7 @@ class plupload
 	/**
 	* Sets the default directories for uploads
 	*
-	* @return null
+	* @return void
 	*/
 	protected function set_default_directories()
 	{
@@ -410,7 +410,7 @@ class plupload
 	* @param string $upload_directory Upload directory
 	* @param string $temporary_directory Temporary directory
 	*
-	* @return null
+	* @return void
 	*/
 	public function set_upload_directories($upload_directory, $temporary_directory)
 	{
diff --git a/phpBB/phpbb/profilefields/type/type_base.php b/phpBB/phpbb/profilefields/type/type_base.php
index 8fe4b38c46..80a535cb1f 100644
--- a/phpBB/phpbb/profilefields/type/type_base.php
+++ b/phpBB/phpbb/profilefields/type/type_base.php
@@ -179,7 +179,6 @@ abstract class type_base implements type_interface
 	*/
 	public function display_options(&$template_vars, &$field_data)
 	{
-		return;
 	}
 
 	/**
diff --git a/phpBB/phpbb/report/controller/report.php b/phpBB/phpbb/report/controller/report.php
index 026f450d85..1af565e6a0 100644
--- a/phpBB/phpbb/report/controller/report.php
+++ b/phpBB/phpbb/report/controller/report.php
@@ -258,7 +258,7 @@ class report
 	 * @param 	array	$error
 	 * @param	string	$s_hidden_fields
 	 * @param	mixed	$captcha
-	 * @return	null
+	 * @return	void
 	 */
 	protected function assign_template_data($mode, $id, $reason_id, $report_text, $user_notify, $error = array(), $s_hidden_fields = '', $captcha = false)
 	{
diff --git a/phpBB/phpbb/session.php b/phpBB/phpbb/session.php
index d311f3758e..0d401c86e1 100644
--- a/phpBB/phpbb/session.php
+++ b/phpBB/phpbb/session.php
@@ -1068,8 +1068,6 @@ class session
 		* @since 3.1.6-RC1
 		*/
 		$phpbb_dispatcher->trigger_event('core.session_gc_after');
-
-		return;
 	}
 
 	/**
@@ -1143,7 +1141,7 @@ class session
 
 		if (defined('IN_CHECK_BAN') || defined('SKIP_CHECK_BAN'))
 		{
-			return;
+			return false;
 		}
 
 		$banned = false;
diff --git a/phpBB/phpbb/storage/controller/attachment.php b/phpBB/phpbb/storage/controller/attachment.php
index 11d254f24a..08cd012290 100644
--- a/phpBB/phpbb/storage/controller/attachment.php
+++ b/phpBB/phpbb/storage/controller/attachment.php
@@ -289,7 +289,7 @@ class attachment extends controller
 	 */
 	protected function filenameFallback($filename)
 	{
-		$filename = preg_replace(['/[^\x20-\x7e]/', '/%/', '/\//', '/\\\/'], '', $filename);
+		$filename = preg_replace(['/[^\x20-\x7e]/', '/%/', '/\//', '/\\\\/'], '', $filename);
 
 		return (!empty($filename)) ?: 'File';
 	}
diff --git a/phpBB/phpbb/template/twig/tokenparser/defineparser.php b/phpBB/phpbb/template/twig/tokenparser/defineparser.php
index 14b885a902..ce394c0896 100644
--- a/phpBB/phpbb/template/twig/tokenparser/defineparser.php
+++ b/phpBB/phpbb/template/twig/tokenparser/defineparser.php
@@ -21,9 +21,8 @@ class defineparser extends \Twig\TokenParser\AbstractTokenParser
 	*
 	* @param \Twig\Token $token A Twig\Token instance
 	*
-	* @return \Twig\Node\Node A Twig\Node instance
 	* @throws \Twig\Error\SyntaxError
-	* @return \phpbb\template\twig\node\definenode
+	* @return \Twig\Node\Node A Twig\Node instance
 	*/
 	public function parse(\Twig\Token $token)
 	{
diff --git a/phpBB/phpbb/textformatter/s9e/renderer.php b/phpBB/phpbb/textformatter/s9e/renderer.php
index 855e034b14..8328b65a95 100644
--- a/phpBB/phpbb/textformatter/s9e/renderer.php
+++ b/phpBB/phpbb/textformatter/s9e/renderer.php
@@ -148,7 +148,7 @@ class renderer implements \phpbb\textformatter\renderer_interface
 	*
 	* @param  \phpbb\config\config $config
 	* @param  \phpbb\path_helper   $path_helper
-	* @return null
+	* @return void
 	*/
 	public function configure_smilies_path(\phpbb\config\config $config, \phpbb\path_helper $path_helper)
 	{
diff --git a/phpBB/phpbb/textreparser/base.php b/phpBB/phpbb/textreparser/base.php
index c4b344f8db..6ac30a0002 100644
--- a/phpBB/phpbb/textreparser/base.php
+++ b/phpBB/phpbb/textreparser/base.php
@@ -40,8 +40,11 @@ abstract class base implements reparser_interface
 	abstract protected function get_records_by_range($min_id, $max_id);
 
 	/**
-	* {@inheritdoc}
-	*/
+	 * Save record
+	 *
+	 * @param array $record
+	 * @return void
+	 */
 	abstract protected function save_record(array $record);
 
 	/**
diff --git a/phpBB/phpbb/user.php b/phpBB/phpbb/user.php
index 2e7ab22651..52427d2915 100644
--- a/phpBB/phpbb/user.php
+++ b/phpBB/phpbb/user.php
@@ -470,14 +470,18 @@ class user extends \phpbb\session
 	* @param $number        int|float   The number we want to get the plural case for. Float numbers are floored.
 	* @param $force_rule    mixed   False to use the plural rule of the language package
 	*                               or an integer to force a certain plural rule
-	* @return int|bool     The plural-case we need to use for the number plural-rule combination, false if $force_rule
+	* @return int|false     The plural-case we need to use for the number plural-rule combination, false if $force_rule
 	* 					   was invalid.
 	*
 	* @deprecated: 3.2.0-dev (To be removed: 4.0.0)
 	*/
 	function get_plural_form($number, $force_rule = false)
 	{
-		return $this->language->get_plural_form($number, $force_rule);
+		try {
+			return $this->language->get_plural_form($number, $force_rule);
+		} catch (\phpbb\language\exception\invalid_plural_rule_exception $e) {
+			return false;
+		}
 	}
 
 	/**
diff --git a/tests/template/template_test_case.php b/tests/template/template_test_case.php
index fc24600799..9a06c06dc9 100644
--- a/tests/template/template_test_case.php
+++ b/tests/template/template_test_case.php
@@ -110,7 +110,7 @@ class phpbb_template_template_test_case extends phpbb_test_case
 				'autoescape'	=> false,
 			)
 		);
-		$this->template = new phpbb\template\twig\twig($path_helper, $config, $context, $twig, $cache_path, $this->user, array(new \phpbb\template\twig\extension($context, $twig, $this->user)));
+		$this->template = new phpbb\template\twig\twig($path_helper, $config, $context, $twig, $cache_path, $this->user, array(new \phpbb\template\twig\extension($context, $twig, $lang)));
 		$twig->setLexer(new \phpbb\template\twig\lexer($twig));
 		$this->template->set_custom_style('tests', $this->template_path);
 	}
diff --git a/tests/text_formatter/s9e/factory_test.php b/tests/text_formatter/s9e/factory_test.php
index 9ab32999d8..7e35c18332 100644
--- a/tests/text_formatter/s9e/factory_test.php
+++ b/tests/text_formatter/s9e/factory_test.php
@@ -15,6 +15,16 @@ require_once __DIR__ . '/../../test_framework/phpbb_database_test_case.php';
 
 class phpbb_textformatter_s9e_factory_test extends phpbb_database_test_case
 {
+	/**
+	 * @var phpbb_mock_cache
+	 */
+	private $cache;
+
+	/**
+	 * @var phpbb_mock_event_dispatcher
+	 */
+	private $dispatcher;
+
 	protected function setUp(): void
 	{
 		$this->cache = new phpbb_mock_cache;