private static ExprNodeDesc propConstDistUDAFParams() {
    return null;
  }
Get Value Keys for RS following MapSide GB

@param GroupByOperator
         MapSide GB
@param outputKeyColumnNames
@param colExprMap
@return List of ExprNodeDesc of Values
@throws SemanticException
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/translator/opconventer/HiveGBOpConvUtil.java