@Override
  public String visitUnquotedIdentifer(PartitionFilterParser.UnquotedIdentiferContext ctx) {
    return ctx.getText();
  }
Override the default behavior for all visit methods. This will only return a non-null result
when the context has only one child. This is done because there is no generic method to
combine the results of the context children. In all other cases null is returned.
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/parser/PartFilterVisitor.java