removing all callbacks from an action results in NULL callback

[sphoid]

If you remove all callbacks for an action and the action is triggered afterwards you will receive a php warning (Warning: call_user_func_array() expects parameter 1 to be a valid callback, no array or string given)

The following code will demonstrate this:

function do_something(){

	echo 'do_something called<br/>';

	do_action( 'test_action_1234', 'test' );

}

function test_action_callback( $param ){

	echo 'test_action happened<br/>';

}
add_action( 'test_action_1234', 'test_action_callback', 10 );

do_something();

remove_action( 'test_action_1234', 'test_action_callback', 10 );

do_something();

This happens on line 427 in wp-includes/plugin.php:

foreach ( (array) current($wp_filter[$tag]) as $the_ )

when $wp_filter['test_action_1234'] is empty it is converted to a single element array that contains a null value which php then complains about not being a valid callback, which makes sense.

Expected behavior is that no warning should occur when all callbacks are removed from an action.

When all tags are removed for an action then the tag should be removed from $wp_filter to prevent this. I am attaching a patch for wp-includes/plugin.php remove_filter function that does this.

[sphoid]

Patch that unsets $wp_filter[$tag] if it contains no callbacks

[wonderboymusic]

In 28884:

After [28883], remove_filter() should set $GLOBALS['wp_filter'][ $tag ] to array() when empty.

Props wonderboymusic, sphoid.
Fixes #28142.