code: public GrpcServiceBuilder addService(BindableService bindableService) {
          if (bindableService instanceof ProtoReflectionService) {
              checkState(protoReflectionService == null,
                         "Attempting to add a ProtoReflectionService but one is already present. " +
                         "ProtoReflectionService must only be added once.");
              protoReflectionService = (ProtoReflectionService) bindableService;
          }
  
          return addService(bindableService.bindService());
      }
docs: Adds a gRPC {@link BindableService} to this {@link GrpcServiceBuilder}. Most gRPC service
  implementations are {@link BindableService}s.