@Override
            protected void writeTo(Output output, T message) throws IOException
            {
                final Collection<Enum<?>> collection = accessor.get(message);
                if (collection != null && !collection.isEmpty())
                {
                    for (Enum<?> en : collection)
                    {
                        if (en != null)
                            eio.writeTo(output, number, true, en);
                    }
                }
            }
For lazy initialization called by {@link RuntimeFieldFactory}.
protostuff-runtime/src/main/java/io/protostuff/runtime/RuntimeRepeatedFieldFactory.java