current-menu-item and current_page_item classes incorrectly added to custom menu items with no URL value.

[tschoonover]

If the current page is the home page, the _wp_menu_item_classes_by_context function will incorrectly add the current-menu-item and current_page_item classes to any custom menu items that do not have a value for URL. This occurs because the custom menu item URL (after formatting) compares equal to the home page URL.

Note - a custom menu item might not have a URL value if it is used as only a parent container for another submenu.

Caused by [18746] for #15954 because $_root_relative_current is an empty string for the home page. We could check if the URL is empty for custom menu items before adding classes.

Attached patch prevents an empty URL from triggering the current-menu-item class.

It also allows a relative root URL ("/") to trigger the current-menu-item class, as before.

In [19657]:

Properly handle a blank nav menu custom URL when determining what page we're on. see #19699 for trunk.

In [19658]:

Properly handle a blank nav menu custom URL when determining what page we're on. fixes #19699 for 3.3