@Override
        public final String getFieldName(int number)
        {
            switch (number)
            {
                case 1:
                    return FIELD_NAME_KEY;
                case 2:
                    return FIELD_NAME_VALUE;
                default:
                    return null;
            }
        }
The pipe schema of the {@link Map}.
protostuff-collectionschema/src/main/java/io/protostuff/MapSchema.java