code: public Optional<MapperInstance> getDeserializer( JType type ) {
          return Optional.fromNullable( deserializers.get( type.getQualifiedSourceName() ) );
      }
docs: Return a {@link MapperInstance} instantiating the deserializer for the given type
  
  @param type a {@link com.google.gwt.core.ext.typeinfo.JType} object.
  @return a {@link com.google.gwt.thirdparty.guava.common.base.Optional} object.