@Override
            protected Object kFrom(Input input,
                    MapWrapper<Object, Object> wrapper) throws IOException
            {
                final Object value = input.mergeObject(wrapper, keySchema);
                if (value != wrapper)
                {
                    // referenced.
                    // An entry would never have a cyclic reference.
                    ((GraphInput) input).updateLast(value, wrapper);
                    return value;
                }

                return wrapper.setValue(null);
            }
Static utility for creating runtime {@link java.util.Map} fields.

@author David Yu
@created Jan 21, 2011
protostuff-runtime/src/main/java/io/protostuff/runtime/RuntimeMapFieldFactory.java