diff --git a/phpBB/install/controller/install.php b/phpBB/install/controller/install.php
index 1217107484..12bc575b83 100644
--- a/phpBB/install/controller/install.php
+++ b/phpBB/install/controller/install.php
@@ -62,6 +62,11 @@ class install
 		$this->installer = $installer;
 	}
 
+	/**
+	 * Controller logic
+	 *
+	 * @return \Symfony\Component\HttpFoundation\Response|StreamedResponse
+	 */
 	public function handle()
 	{
 		// @todo check that phpBB is not already installed
@@ -82,8 +87,7 @@ class install
 
 		if ($this->request->is_ajax())
 		{
-			$installer = &$this->installer;
-
+			$installer = $this->installer;
 			$response = new StreamedResponse();
 			$response->setCallback(function() use ($installer) {
 				$installer->run();
diff --git a/phpBB/install/helper/iohandler/iohandler_base.php b/phpBB/install/helper/iohandler/iohandler_base.php
index 0d5467d202..c0e6921fb2 100644
--- a/phpBB/install/helper/iohandler/iohandler_base.php
+++ b/phpBB/install/helper/iohandler/iohandler_base.php
@@ -62,8 +62,6 @@ abstract class iohandler_base implements iohandler_interface
 	 * Set language service
 	 *
 	 * @param \phpbb\language\language $language
-	 *
-	 * @return null
 	 */
 	public function set_language(\phpbb\language\language $language)
 	{
diff --git a/phpBB/install/helper/iohandler/iohandler_interface.php b/phpBB/install/helper/iohandler/iohandler_interface.php
index cea5610586..387a8617b9 100644
--- a/phpBB/install/helper/iohandler/iohandler_interface.php
+++ b/phpBB/install/helper/iohandler/iohandler_interface.php
@@ -74,8 +74,6 @@ interface iohandler_interface
 	 * @param string|array		$error_title		Title of the error message.
 	 * @param string|bool|array	$error_description	Description of the error (and possibly guidelines to resolve it),
 	 * 												or false if the error description is not available.
-	 *
-	 * @return null
 	 */
 	public function add_error_message($error_title, $error_description = false);
 
@@ -85,11 +83,9 @@ interface iohandler_interface
 	 * Note: When an array is passed into the parameters below, it will be
 	 * resolved as printf($param[0], $param[1], ...).
 	 *
-	 * @param string|array		$warning_title			Title of the error message
-	 * @param string|bool|array	$warning_description	Description of the error (and possibly guidelines to resolve it),
+	 * @param string|array		$warning_title			Title of the warning message
+	 * @param string|bool|array	$warning_description	Description of the warning (and possibly guidelines to resolve it),
 	 * 													or false if the error description is not available
-	 *
-	 * @return null
 	 */
 	public function add_warning_message($warning_title, $warning_description = false);
 
@@ -99,11 +95,9 @@ interface iohandler_interface
 	 * Note: When an array is passed into the parameters below, it will be
 	 * resolved as printf($param[0], $param[1], ...).
 	 *
-	 * @param string|array		$log_title			Title of the error message
-	 * @param string|bool|array	$log_description	Description of the error (and possibly guidelines to resolve it),
+	 * @param string|array		$log_title			Title of the log message
+	 * @param string|bool|array	$log_description	Description of the log (and possibly guidelines to resolve it),
 	 * 												or false if the error description is not available
-	 *
-	 * @return null
 	 */
 	public function add_log_message($log_title, $log_description = false);
 
@@ -112,8 +106,21 @@ interface iohandler_interface
 	 *
 	 * @param string	$title	Language variable with the title of the form
 	 * @param array		$form	An array describing the required data (options etc)
-	 *
-	 * @return null
 	 */
 	public function add_user_form_group($title, $form);
+
+	/**
+	 * Sets the number of tasks belonging to the installer in the current mode.
+	 *
+	 * @param int	$task_count	Number of tasks
+	 */
+	public function set_task_count($task_count);
+
+	/**
+	 * Sets the progress information
+	 *
+	 * @param string	$task_lang_key	Language key for the name of the task
+	 * @param int		$task_number	Position of the current task in the task queue
+	 */
+	public function set_progress($task_lang_key, $task_number);
 }
diff --git a/phpBB/install/installer.php b/phpBB/install/installer.php
index 5a2fcc4d85..34bc4b23f7 100644
--- a/phpBB/install/installer.php
+++ b/phpBB/install/installer.php
@@ -60,8 +60,6 @@ class installer
 
 	/**
 	 * Run phpBB installer
-	 *
-	 * @return null
 	 */
 	public function run()
 	{
diff --git a/phpBB/install/module/obtain_data/task/obtain_admin_data.php b/phpBB/install/module/obtain_data/task/obtain_admin_data.php
index d820353880..6745419eb2 100644
--- a/phpBB/install/module/obtain_data/task/obtain_admin_data.php
+++ b/phpBB/install/module/obtain_data/task/obtain_admin_data.php
@@ -63,8 +63,6 @@ class obtain_admin_data extends \phpbb\install\task_base implements \phpbb\insta
 
 	/**
 	 * Process form data
-	 *
-	 * @return null
 	 */
 	protected function process_form()
 	{
@@ -93,8 +91,6 @@ class obtain_admin_data extends \phpbb\install\task_base implements \phpbb\insta
 	 *
 	 * @param bool $use_request_data Whether to use submited data
 	 *
-	 * @return null
-	 *
 	 * @throws \phpbb\install\exception\user_interaction_required_exception When the user is required to provide data
 	 */
 	protected function request_form_data($use_request_data = false)
diff --git a/phpBB/install/module/obtain_data/task/obtain_board_data.php b/phpBB/install/module/obtain_data/task/obtain_board_data.php
index e17ecd01c5..5415d152a7 100644
--- a/phpBB/install/module/obtain_data/task/obtain_board_data.php
+++ b/phpBB/install/module/obtain_data/task/obtain_board_data.php
@@ -71,8 +71,6 @@ class obtain_board_data extends \phpbb\install\task_base implements \phpbb\insta
 
 	/**
 	 * Process form data
-	 *
-	 * @return null
 	 */
 	protected function process_form()
 	{
diff --git a/phpBB/install/module/obtain_data/task/obtain_database_data.php b/phpBB/install/module/obtain_data/task/obtain_database_data.php
index 4c71c4adea..c8bdff4bf8 100644
--- a/phpBB/install/module/obtain_data/task/obtain_database_data.php
+++ b/phpBB/install/module/obtain_data/task/obtain_database_data.php
@@ -71,8 +71,6 @@ class obtain_database_data extends \phpbb\install\task_base implements \phpbb\in
 
 	/**
 	 * Process form data
-	 *
-	 * @return null
 	 */
 	protected function process_form()
 	{
@@ -110,8 +108,6 @@ class obtain_database_data extends \phpbb\install\task_base implements \phpbb\in
 	 *
 	 * @param bool $use_request_data Whether to use submited data
 	 *
-	 * @return null
-	 *
 	 * @throws \phpbb\install\exception\user_interaction_required_exception When the user is required to provide data
 	 */
 	protected function request_form_data($use_request_data = false)
diff --git a/phpBB/install/module/requirements/task/check_filesystem.php b/phpBB/install/module/requirements/task/check_filesystem.php
index 0314a988f1..1c76ed146e 100644
--- a/phpBB/install/module/requirements/task/check_filesystem.php
+++ b/phpBB/install/module/requirements/task/check_filesystem.php
@@ -122,7 +122,6 @@ class check_filesystem extends \phpbb\install\task_base
 	 * Sets $this->tests_passed
 	 *
 	 * @param	bool	$is_passed
-	 * @return null
 	 */
 	protected function set_test_passed($is_passed)
 	{
diff --git a/phpBB/install/module/requirements/task/check_server_environment.php b/phpBB/install/module/requirements/task/check_server_environment.php
index 797083d429..4bfea57b0e 100644
--- a/phpBB/install/module/requirements/task/check_server_environment.php
+++ b/phpBB/install/module/requirements/task/check_server_environment.php
@@ -81,7 +81,6 @@ class check_server_environment extends \phpbb\install\task_base
 	 * Sets $this->tests_passed
 	 *
 	 * @param	bool	$is_passed
-	 * @return null
 	 */
 	protected function set_test_passed($is_passed)
 	{
@@ -91,8 +90,6 @@ class check_server_environment extends \phpbb\install\task_base
 
 	/**
 	 * Check if the requirements for PHP version is met
-	 *
-	 * @return null
 	 */
 	protected function check_php_version()
 	{
@@ -111,8 +108,6 @@ class check_server_environment extends \phpbb\install\task_base
 
 	/**
 	 * Checks if the installed PHP has getimagesize() available
-	 *
-	 * @return null
 	 */
 	protected function check_image_size()
 	{
@@ -129,8 +124,6 @@ class check_server_environment extends \phpbb\install\task_base
 
 	/**
 	 * Checks if the installed PHP supports PCRE
-	 *
-	 * @return null
 	 */
 	protected function check_pcre()
 	{
@@ -147,8 +140,6 @@ class check_server_environment extends \phpbb\install\task_base
 
 	/**
 	 * Checks whether PHP's JSON extension is available or not
-	 *
-	 * @return null
 	 */
 	protected function check_json()
 	{
@@ -165,8 +156,6 @@ class check_server_environment extends \phpbb\install\task_base
 
 	/**
 	 * Check if any supported DBMS is available
-	 *
-	 * @return null
 	 */
 	protected function check_available_dbms()
 	{
diff --git a/phpBB/install/module_base.php b/phpBB/install/module_base.php
index defccaefef..a34a103aca 100644
--- a/phpBB/install/module_base.php
+++ b/phpBB/install/module_base.php
@@ -63,8 +63,6 @@ abstract class module_base implements module_interface
 	 * @param \Symfony\Component\DependencyInjection\ContainerInterface	$container
 	 * @param \phpbb\install\helper\config								$config
 	 * @param \phpbb\install\helper\iohandler\iohandler_interface		$iohandler
-	 *
-	 * @return null
 	 */
 	public function setup(\Symfony\Component\DependencyInjection\ContainerInterface $container, \phpbb\install\helper\config $config, \phpbb\install\helper\iohandler\iohandler_interface $iohandler)
 	{