@Override
  public Object getField(final Object o) {
    if (o == null) {
      return null;
    }
    return ((TUnion<? extends TUnion<?, ?>, ? extends TFieldIdEnum>) o).getFieldValue();
  }
Always use the ObjectInspectorFactory to create new ObjectInspector objects,
instead of directly creating an instance of this class.
serde/src/java/org/apache/hadoop/hive/serde2/objectinspector/ThriftUnionObjectInspector.java