@Override
        protected void transfer(Pipe pipe, Input input, Output output)
                throws IOException
        {
            transferObject(this, pipe, input, output, strategy);
        }
Used when the type is an interface (Map/SortedMap).

@author David Yu
@created Apr 24, 2012
protostuff-runtime/src/main/java/io/protostuff/runtime/PolymorphicMapSchema.java