message: Return failed status when client not found.
diff: @@ -71,6 +71,10 @@ class GrpcEagerClientCache : public EagerClientCache {
  if (it == clients_.end()) {
  tensorflow::SharedGrpcChannelPtr shared =
  cache_->FindWorkerChannel(target);
  + if (shared == nullptr) {
  + return errors::InvalidArgument("Client for target ", target,
  + " not found.");
  + }
  auto worker = std::unique_ptr<EagerClient>(new GrpcEagerClient(
  shared, threads_[AssignClientToThread(target)].completion_queue()));
  