@Override
  public Object evaluate(DeferredObject[] arguments) throws HiveException {
    Object arg0 = arguments[0].get();
    Object arg1 = arguments[1].get();
    Object value0 = returnOIResolver.convertIfNecessary(arg0, argumentOIs[0], false);
    if (arg0 == null || arg1 == null) {
      return value0;
    }
    Object value1 = returnOIResolver.convertIfNecessary(arg1, argumentOIs[1], false);
    ObjectInspector compareOI = returnOIResolver.get();
    if (ObjectInspectorUtils.compare(value0, compareOI, value1, compareOI) == 0) {
      return null;
    }
    return value0;
  }
GenericUDF Class for SQL construct "nullif(a,b)".
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFNullif.java