public static boolean isNullConstant(ExprNodeDesc value) {
    if ((value instanceof ExprNodeConstantDesc)
        && ((ExprNodeConstantDesc) value).getValue() == null) {
      return true;
    }
    return false;
  }
Get Map of ExprNodeColumnDesc HashCode to ExprNodeColumnDesc.

@param exprDesc
@param hashCodeToColumnDescMap
ql/src/java/org/apache/hadoop/hive/ql/plan/ExprNodeDescUtils.java