code: public static String getGrpcUserAgent(
        String transportName, @Nullable String applicationUserAgent) {
      StringBuilder builder = new StringBuilder();
      if (applicationUserAgent != null) {
        builder.append(applicationUserAgent);
        builder.append(' ');
      }
      builder.append("grpc-java-");
      builder.append(transportName);
      builder.append('/');
      builder.append(IMPLEMENTATION_VERSION);
      return builder.toString();
    }
docs: Gets the User-Agent string for the gRPC transport.