@Override
  public String getDisplayString(String[] children) {
    assert (children.length == 1);
    return getStandardDisplayString("evaluate_npe", children);
  }
GenericUDFEvaluateNPE
This UDF is to throw an Null Pointer Exception
It is used to test hive failure handling
itests/util/src/main/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFEvaluateNPE.java