private void checkNotNull(Object object, String msg) {
    if(object == null) {
      throw new NullPointerException(msg);
    }
  }
GenericUDFMacro wraps a user-defined macro expression into a GenericUDF
interface.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFMacro.java