[ticket/16955] Fix most return types in phpdoc

PHPBB3-16955

phpBB/phpbb/db/migration/profilefield_base_migration.php

@@ -183,8 +183,8 @@ abstract class profilefield_base_migration extends container_aware_migration
 	}
 
 	/**
-	* @param int			$start		Start of staggering step
-	* @return		mixed		int start of the next step, null if the end was reached
+	* @param	int			$start		Start of staggering step
+	* @return	int|null	int start of the next step, null if the end was reached
 	*/
 	public function convert_user_field_to_custom_field($start)
 	{
@@ -226,7 +226,7 @@ abstract class profilefield_base_migration extends container_aware_migration
 		if ($converted_users < $limit)
 		{
 			// No more users left, we are done...
-			return;
+			return null;
 		}
 
 		return $start + $limit;

phpBB/phpbb/db/migration/tool/config_text.php

@@ -63,7 +63,7 @@ class config_text implements \phpbb\db\migration\tool\tool_interface
 	* @param string $config_name The name of the config_text setting you would
 	* 	like to update
 	* @param mixed $config_value The value of the config_text setting
-	* @return null
+	* @return void
 	* @throws \phpbb\db\migration\exception
 	*/
 	public function update($config_name, $config_value)