Akka.Streams.Tests.Dsl.FlowSelectAsyncSpec.A_Flow_with_SelectAsync_must_signal_NPE_when_task_is_completed_with_null C# (CSharp) Method

        public void A_Flow_with_SelectAsync_must_signal_NPE_when_task_is_completed_with_null()
        {
            var c = TestSubscriber.CreateManualProbe<string>(this);

            Source.From(new[] {"a", "b"})
                .SelectAsync(4, _ => Task.FromResult(null as string))
                .To(Sink.FromSubscriber(c)).Run(Materializer);

            var sub = c.ExpectSubscription();
            sub.Request(10);
            c.ExpectError().Message.Should().StartWith(ReactiveStreamsCompliance.ElementMustNotBeNullMsg);
        }