Allow methods with no bindings. Fixes #263 (#267)

Author: tmc

examples/examplepb/a_bit_of_everything.pb.go

@@ -115,6 +115,7 @@ service ABitOfEverythingService {
 			body: "*"
 		};
 	}
+	rpc NoBindings(google.protobuf.Empty) returns (google.protobuf.Empty) {}
 	rpc Timeout(google.protobuf.Empty) returns (google.protobuf.Empty) {
 		option (google.api.http) = {
 			get: "/v2/example/timeout",

examples/examplepb/a_bit_of_everything.proto

@@ -221,6 +221,10 @@ func (s *_ABitOfEverythingServer) DeepPathEcho(ctx context.Context, msg *example
 	return msg, nil
 }
 
+func (s *_ABitOfEverythingServer) NoBindings(ctx context.Context, msg *empty.Empty) (*empty.Empty, error) {
+	return nil, nil
+}
+
 func (s *_ABitOfEverythingServer) Timeout(ctx context.Context, msg *empty.Empty) (*empty.Empty, error) {
 	select {
 	case <-ctx.Done():