Helper Methods for Filters
WordPress offers some helper methods for filters. If you want to pass true or false to a filter, you can use:
add_filter('my_filter', '__return_true');
add_filter('my_filter', '__return_false');
Other available filter helper methods are:
add_filter('my_filter', '__return_empty_array');
add_filter('my_filter', '__return_zero');
add_filter('my_filter', '__return_null');
add_filter('my_filter', '__return_empty_string');