PHP Strict: WP_Customize_Filter_Setting::update() incompatible with parent method

[kurtpayne]

Full strict message:

Declaration of WP_Customize_Filter_Setting::update() should be compatible with that of WP_Customize_Setting::update()

This is happening because the declaration of WP_Customize_Filter_Setting::update doesn't accept a parameter.

On a different note, the original declaration of WP_Customize_Setting::update is protected. The visibility is changed to public, though, in WP_Customize_Filter_Setting, WP_Customize_Header_Image_Setting, and WP_Customize_Background_Image_Setting.

In 22448:

Ensure a method is compatible with its parent. props kurtpayne, fixes #22265.