Ticket #45903: 45903.1.diff

src/wp-content/themes/twentynineteen/js/priority-menu.js

@@ -116 +116 @@
                 }
 
                 // Adds the necessary UI to operate the menu.
-                var visibleList  = container.parentNode.querySelector('.main-menu[id]');
-                var hiddenList   = visibleList.parentNode.nextElementSibling.querySelector('.hidden-links');
-                var toggleButton = visibleList.parentNode.nextElementSibling.querySelector('.main-menu-more-toggle');
+                var visibleList        = container.parentNode.querySelector('.main-menu[id]');
+                var nextElementSibling = visibleList.parentNode.nextElementSibling;
+                var hiddenList   = nextElementSibling.querySelector('.hidden-links');
+                var toggleButton = nextElementSibling.querySelector('.main-menu-more-toggle');
+
+                if ( ! nextElementSibling ) {
+                        return;
+                }
 
                 if ( isOverflowingNavivation( visibleList, toggleButton, container ) ) {
 

src/wp-content/themes/twentynineteen/js/touch-keyboard-navigation.js

@@ -284 +284 @@
                                 var prevLi            = getCurrentParent( event.target, '.main-navigation > div > ul > li', '.main-navigation' ).previousElementSibling;
                                 var nextLi            = getCurrentParent( event.target, '.main-navigation > div > ul > li', '.main-navigation' ).nextElementSibling;
 
+                                if ( ! currentDivSibling ) {
+                                        return;
+                                }
+
                                 if ( null !== focusedElement && null !== hasClass( focusedElement, focusedClass ) ) {
                                         deleteClass( focusedElement, focusedClass );
                                 }