code: @Override
    public <ReqT, RespT> ClientCall<ReqT, RespT> newCall(
        MethodDescriptor<ReqT, RespT> methodDescriptor, CallOptions callOptions) {
      Preconditions.checkState(!shutdown, "Cannot perform operations on a closed connection");
      return getNextChannel().newCall(methodDescriptor, callOptions);
    }
docs: {@inheritDoc}
  <P>
  Create a {@link ClientCall} on a Channel from the pool chosen in a round-robin fashion to the
  remote operation specified by the given {@link MethodDescriptor}. The returned
  {@link ClientCall} does not trigger any remote behavior until
  {@link ClientCall#start(ClientCall.Listener, io.grpc.Metadata)} is invoked.