@Override
 public QueryNode visit(FunctionCallNode leftNode) {
   return mRightNode.accept(new FunctionCallNodeMerger(leftNode));
 }
 @Override
 public QueryNode visit(FieldNode leftNode) {
   return mRightNode.accept(new FieldNodeMerger(leftNode));
 }
 @Override
 public QueryNode visit(BinaryOperatorNode leftNode) {
   return mRightNode.accept(new BinaryOperatorNodeMerger(leftNode));
 }
 @Override
 public QueryNode visit(ConstantNode leftNode) {
   return mRightNode.accept(new ConstantNodeMerger(leftNode));
 }