Merge branch 'ss/fix-milestone-dropdown-error' into 'master'

Resolve no search result click causing issue

See merge request gitlab-org/gitlab!32698

app/assets/javascripts/milestone_select.js

@@ -130,10 +130,13 @@ export default class MilestoneSelect {
         fieldName: $dropdown.data('fieldName'),
         text: milestone => escape(milestone.title),
         id: milestone => {
+          if (milestone !== undefined) {
             if (!useId && !$dropdown.is('.js-issuable-form-dropdown')) {
               return milestone.name;
             }
+
             return milestone.id;
+          }
         },
         hidden: () => {
           $selectBox.hide();