You can implement emptiness with the wrapper message types, e.g. StringValue: https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/wrappe

You can implement emptiness with the wrapper message types, e.g. StringValue: https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/wrappers.proto https://github.com/protocolbuffers/protobuf/blob/master/src/... and sometimes defining your own, e.g. nullable lists. It's not elegant, but it is simple.