@Override
  public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
    initializeInput(arguments);
    return PrimitiveObjectInspectorFactory.writableLongObjectInspector;
  }
deterministic version of UDFUnixTimeStamp. enforces argument
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFToUnixTimeStamp.java