Refactor create_function

There is an inbuilt function for returning null: __return_null.

So you can replace create_function('$a', 'return null;'); with just '__return_null' (note the quotes) as it seems $a is not used anyway.

Or you can use an anonymous function as the argument directly: function($a) {return null;} (no quotes). Either way since the argument is expecting a function calback.