class GrpcServerRequest extends RpcServerRequest implements GrpcRequest {

  @Override protected String propagationField(String keyName) {
    if (keyName == null) throw new NullPointerException("keyName == null");
    Key<String> key = nameToKey.get(keyName);
    if (key == null) {
      assert false : "We currently don't support getting headers except propagation fields";
      return null;
    }
    return headers.get(key);
  }

    GrpcServerRequest(Map<String, Key<String>> nameToKey, ServerCall<?, ?> call, Metadata headers);

}