public void accept(TreeVisitor treeVisitor) throws MetaException {
    if (this.root != null) {
      this.root.accept(treeVisitor);
    }
  }
Validates and gets the query parameter for JDO filter pushdown based on the column
and the constant stored in this node.
@param partitionKeys
@param partColIndex The index of the column to check.
@param filterBuilder filter builder used to report error, if any.
@return The parameter string.
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/parser/ExpressionTree.java