Merge pull request #4581 from DSpace/backport-4536-to-dspace-9_x

[Port dspace-9_x] Fix empty search query after previous non-empty search

Author: tdonohue

src/app/core/shared/search/search-configuration.service.ts

@@ -183,7 +183,7 @@ export class SearchConfigurationService implements OnDestroy {
    */
   getCurrentQuery(defaultQuery: string) {
     return this.routeService.getQueryParameterValue('query').pipe(map((query) => {
-      return query || defaultQuery;
+      return query !== null ? query : defaultQuery; // Allow querying when the value is empty
     }));
   }