@Override
                public void writeTo(Output output, T message)
                        throws IOException
                {
                    final Enum<?> existing = (Enum<?>) us.getObject(message,
                            offset);
                    if (existing != null)
                        eio.writeTo(output, number, repeated, existing);
                }
Field factory via sun.misc.Unsafe.

@author David Yu
@created Jul 7, 2011
protostuff-runtime/src/main/java/io/protostuff/runtime/RuntimeUnsafeFieldFactory.java