fix: avoid nullpointer when gvariants return empty results

Author: brunopacheco1

src/main/java/io/github/genomicdatainfrastructure/discovery/datasets/infrastructure/beacon/persistence/BeaconGVariantsRequestMapper.java

@@ -50,7 +50,7 @@ public static List<GVariantsSearchResponse> map(BeaconResponse response) {
     }
 
     private static GVariantsSearchResponse mapResultSetToVariant(BeaconResultSet resultSet) {
-        if (resultSet == null) {
+        if (resultSet == null || resultSet.getResults() == null) {
             return null;
         }
         GVariantsSearchResponse variant = new GVariantsSearchResponse();