front: Add TODO for empty array return in region API.

Added a TODO comment in the API for regions to return an empty array
instead of null when the response status is 204 (No Content).

Issue: #189

Signed-off-by: Nikolay Martyanov <ohmspectator@gmail.com>

frontend/src/api/index.js

@@ -34,6 +34,7 @@ export const fetchSubregions = async (regionId, hierarchyId) => {
   try {
     const response = await api.get(`/api/regions/${regionId}/subregions`, { params: { hierarchyId } });
     if (response.status === 204) {
+      // TODO return empty array instead of null, Issue #189
       return null;
     }
     return response.data;