@Override
            protected void putValueFrom(Input input, MapWrapper<K, V> wrapper,
                    K key) throws IOException
            {
                vPutFrom(input, wrapper, key);
            }
Since we cannot inherit multiple classes, we create this Map schema simply to delegate to the wrapping class'
abstract methods.
protostuff-runtime/src/main/java/io/protostuff/runtime/RuntimeMapField.java