RelationQueryNode isNull
= factory.createRelationQueryNode(queryNode,
RelationQueryNode.OPERATION_NULL);
applyRelativePath(isNull);
node.childrenAccept(this, isNull);
NotQueryNode notNode = (NotQueryNode) queryNode;
NAryQueryNode parent = (NAryQueryNode) notNode.getParent();
parent.removeOperand(notNode);
parent.addOperand(isNull);
} else {
// not null expression
RelationQueryNode notNull =