code: public ServiceDiscovery<T> build()
      {
          if ( serializer == null )
          {
              serializer(new JsonInstanceSerializer<T>(payloadClass));
          }
          if ( serviceDefinitionSerializer == null)
          {
              serializer(new FastjsonServiceDefinitionSerializer<>(payloadClass));
          }
          return new ServiceDiscoveryImpl<T>(client, basePath, serializer, serviceDefinitionSerializer, thisInstance, watchInstances);
      }
docs: Build a new getGroup discovery with the currently set values. If not set, the builder will be
  defaulted with a {@link JsonInstanceSerializer}.
  
  @return new getGroup discovery