code: public Mapper getMapper(Type type) {
      Mapper mapper = cache.get(type);
      if (mapper == null) {
        mapper = createMapper(type);
      }
      return mapper;
    }
docs: Returns a mapper for the given type. If a mapper that can handle given type exists in the
  cache, it will be returned. Otherwise, a new mapper will be created.
  
  @param type
  the type of field in the model class
  @return a {@link Mapper} that is capable of mapping the given type.