code: @Override
      public DBObject getUpdateClause() {
          if (clear) {
              // If clear() was called, updates will either be an empty Map or added items with prefix-less keys
              return new BasicDBObject($set.name(), new BasicDBObject(getNameFromPrefix(), updates));
          } else if (operation == null) {
              return new BasicDBObject();     // If there are no updates, return an empty DBObject
          } else {
              return new BasicDBObject(operation.name(), updates);
          }
      }
docs: -------------------------------------------------------------