Fix tree generation when filtering by name

app/assets/javascripts/groups/stores/groups_store.js

@@ -33,7 +33,8 @@ export default class GroupsStore {
     Object.keys(mappedGroups).forEach((key) => {
       const currentGroup = mappedGroups[key];
       // If the group is not at the root level, add it to its parent array of subGroups.
-      if (currentGroup.parentId) {
+      const parentGroup = mappedGroups[currentGroup['parentId']];
+      if (currentGroup.parentId && parentGroup) {
         mappedGroups[currentGroup.parentId].subGroups[currentGroup.id] = currentGroup;
         mappedGroups[currentGroup.parentId].isOpen = true; // Expand group if it has subgroups
       } else {