code: public JsonObject removeNulls(JsonObject object) {
          for (int j = 0; j < object.names().size(); j++) {
              if (JsonType.OBJECT.equals(object.get(object.names().get(j)).getType())) {
                  removeNulls(object.get(object.names().get(j)).asObject());
              } else {
                  if (object.get(object.names().get(j)).isNull()) {
                      object.set(object.names().get(j), "TO_BE_NULL");
                  }
              }
          }
          return object;
      }
docs: Eliminates null occurrences, replacing them with "TO_BE_NULL"
  
  @param object JsonObject containing json where to replace null ocurrences
  @return JsonObject