Fix errors when board sidebar is closed

app/assets/javascripts/boards/stores/getters.js

@@ -16,7 +16,7 @@ export default {
   },
 
   activeBoardItem: (state) => {
-    return state.boardItems[state.activeId] || {};
+    return state.boardItems[state.activeId] || { iid: '', id: '', fullId: '' };
   },
 
   groupPathForActiveIssue: (_, getters) => {

app/assets/javascripts/sidebar/components/date/sidebar_date_widget.vue

@@ -149,6 +149,9 @@ export default {
     },
   },
   methods: {
+    epicDatePopoverEl() {
+      return this.$refs?.epicDatePopover?.$el;
+    },
     closeForm() {
       this.$refs.editable.collapse();
       this.$el.dispatchEvent(hideDropdownEvent);
@@ -249,12 +252,7 @@ export default {
         :aria-label="$options.i18n.help"
         data-testid="inherit-date-popover"
       />
-      <gl-popover
-        :target="() => $refs.epicDatePopover.$el"
-        triggers="focus"
-        placement="left"
-        boundary="viewport"
-      >
+      <gl-popover :target="epicDatePopoverEl" triggers="focus" placement="left" boundary="viewport">
         <p>{{ $options.i18n.dateHelpValidMessage }}</p>
         <gl-link :href="$options.dateHelpUrl" target="_blank">{{
           $options.i18n.learnMore

spec/frontend/boards/stores/getters_spec.js

@@ -92,7 +92,7 @@ describe('Boards - Getters', () => {
     it.each`
       id     | expected
       ${'1'} | ${'issue'}
-      ${''}  | ${{}}
+      ${''}  | ${{ id: '', iid: '', fullId: '' }}
     `('returns $expected when $id is passed to state', ({ id, expected }) => {
       const state = { boardItems: { 1: 'issue' }, activeId: id };