XWIKI-13337: Dropdown menus don't open in some conditions.

xwiki-platform-core/xwiki-platform-flamingo/xwiki-platform-flamingo-skin/xwiki-platform-flamingo-skin-resources/src/main/resources/flamingo/flamingo.js

@@ -3,19 +3,22 @@ require(['jquery', 'bootstrap'], function($) {
 
     // Fix the bad location of the dropdown menu when the trigger is close to the end of the screen.
     // See: http://jira.xwiki.org/browse/XWIKI-12609
-    $(document).on('shown.bs.dropdown', function (event, data) {
-      var toggle    = $(data.relatedTarget);
+    $(document).on('shown.bs.dropdown', function (event) {
+      var toggle    = $(event.relatedTarget);
       var menu      = toggle.next('.dropdown-menu');
-      var menuWidth = menu.outerWidth();
-      // if the right corner of the menu is after the end of the screen
-      if (menu.offset().left + menuWidth > $(document.body).outerWidth()) {
-        // we put that corner at the same place than the toggle's right corner
-        var newLocation = toggle.offset().left + toggle.outerWidth() - menuWidth;
-        // but don't put it negative, or the user will have to scroll to the left!
-        if (newLocation < 0) {
-          newLocation = 0;
+      // The menu might be not found if it is not located where it is expected.
+      if (menu.length > 0) {
+        var menuWidth = menu.outerWidth();
+        // if the right corner of the menu is after the end of the screen
+        if (menu.offset().left + menuWidth > $(document.body).outerWidth()) {
+          // we put that corner at the same place than the toggle's right corner
+          var newLocation = toggle.offset().left + toggle.outerWidth() - menuWidth;
+          // but don't put it negative, or the user will have to scroll to the left!
+          if (newLocation < 0) {
+            newLocation = 0;
+          }
+          menu.offset({'left': newLocation});
         }
-        menu.offset({'left': newLocation});
       }
     });