Fix StreamRefSerializer NRE bug (#7333)

* Fix StreamRefSerializer NRE bug

* Update API Approval list

src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveStreams.DotNet.verified.txt

@@ -4753,6 +4753,7 @@ namespace Akka.Streams.Implementation.Stages
 }
 namespace Akka.Streams.Serialization
 {
+    [System.Runtime.CompilerServices.NullableAttribute(0)]
     public sealed class StreamRefSerializer : Akka.Serialization.SerializerWithStringManifest
     {
         public StreamRefSerializer(Akka.Actor.ExtendedActorSystem system) { }

src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveStreams.Net.verified.txt

@@ -4727,6 +4727,7 @@ namespace Akka.Streams.Implementation.Stages
 }
 namespace Akka.Streams.Serialization
 {
+    [System.Runtime.CompilerServices.NullableAttribute(0)]
     public sealed class StreamRefSerializer : Akka.Serialization.SerializerWithStringManifest
     {
         public StreamRefSerializer(Akka.Actor.ExtendedActorSystem system) { }

src/core/Akka.Streams.Tests/Serialization/StreamRefSerializer.cs

@@ -0,0 +1,42 @@
+// -----------------------------------------------------------------------
+//  <copyright file="StreamRefSerializer.cs" company="Akka.NET Project">
+//      Copyright (C) 2009-2024 Lightbend Inc. <http://www.lightbend.com>
+//      Copyright (C) 2013-2024 .NET Foundation <https://github.com/akkadotnet/akka.net>
+//  </copyright>
+// -----------------------------------------------------------------------
+
+using System;
+using Akka.Serialization;
+using Akka.Streams.Implementation.StreamRef;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+using static FluentAssertions.FluentActions;
+
+namespace Akka.Streams.Tests.Serialization;
+
+public class StreamRefSerializer: Akka.TestKit.Xunit2.TestKit
+{
+    public StreamRefSerializer(ITestOutputHelper output) 
+        : base(ActorMaterializer.DefaultConfig(), nameof(StreamRefSerializer), output)
+    {
+    }
+
+    [Fact(DisplayName = "StreamRefSerializer should not throw NRE when configuration were set before ActorSystem started")]
+    public void StreamsConfigBugTest()
+    {
+        var message = new SequencedOnNext(10, "test");
+        var serializer = (SerializerWithStringManifest)Sys.Serialization.FindSerializerFor(message);
+        var manifest = serializer.Manifest(message);
+
+        byte[] bytes = null;
+        Invoking(() =>
+        {
+            bytes = serializer.ToBinary(message); // This throws an NRE in the bug
+        }).Should().NotThrow<NullReferenceException>();
+
+        var deserialized = (SequencedOnNext) serializer.FromBinary(bytes, manifest);
+        deserialized.SeqNr.Should().Be(message.SeqNr);
+        deserialized.Payload.Should().Be(message.Payload);
+    }
+}

src/core/Akka.Streams/Serialization/StreamRefSerializer.cs

@@ -10,7 +10,6 @@
 using Akka.Actor;
 using Akka.Serialization;
 using Akka.Streams.Serialization.Proto.Msg;
-using Akka.Util;
 using Google.Protobuf;
 using Akka.Streams.Implementation.StreamRef;
 using CumulativeDemand = Akka.Streams.Implementation.StreamRef.CumulativeDemand;
@@ -19,12 +18,12 @@
 using RemoteStreamFailure = Akka.Streams.Implementation.StreamRef.RemoteStreamFailure;
 using SequencedOnNext = Akka.Streams.Implementation.StreamRef.SequencedOnNext;
 
+#nullable enable
 namespace Akka.Streams.Serialization
 {
     public sealed class StreamRefSerializer : SerializerWithStringManifest
     {
         private readonly ExtendedActorSystem _system;
-        private readonly Akka.Serialization.Serialization _serialization;
 
         private const string SequencedOnNextManifest = "A";
         private const string CumulativeDemandManifest = "B";
@@ -37,52 +36,51 @@ public sealed class StreamRefSerializer : SerializerWithStringManifest
         public StreamRefSerializer(ExtendedActorSystem system) : base(system)
         {
             _system = system;
-            _serialization = system.Serialization;
         }
 
         public override string Manifest(object o)
         {
-            switch (o)
+            return o switch
             {
-                case SequencedOnNext _: return SequencedOnNextManifest;
-                case CumulativeDemand _: return CumulativeDemandManifest;
-                case OnSubscribeHandshake _: return OnSubscribeHandshakeManifest;
-                case RemoteStreamFailure _: return RemoteSinkFailureManifest;
-                case RemoteStreamCompleted _: return RemoteSinkCompletedManifest;
-                case SourceRefImpl _: return SourceRefManifest;
-                case SinkRefImpl _: return SinkRefManifest;
-                default: throw new ArgumentException($"Unsupported object of type {o.GetType()}", nameof(o));
-            }
+                SequencedOnNext => SequencedOnNextManifest,
+                CumulativeDemand => CumulativeDemandManifest,
+                OnSubscribeHandshake => OnSubscribeHandshakeManifest,
+                RemoteStreamFailure => RemoteSinkFailureManifest,
+                RemoteStreamCompleted => RemoteSinkCompletedManifest,
+                SourceRefImpl => SourceRefManifest,
+                SinkRefImpl => SinkRefManifest,
+                _ => throw new ArgumentException($"Unsupported object of type {o.GetType()}", nameof(o))
+            };
         }
 
         public override byte[] ToBinary(object o)
         {
-            switch (o)
+            return o switch
             {
-                case SequencedOnNext onNext: return SerializeSequencedOnNext(onNext).ToByteArray();
-                case CumulativeDemand demand: return SerializeCumulativeDemand(demand).ToByteArray();
-                case OnSubscribeHandshake handshake: return SerializeOnSubscribeHandshake(handshake).ToByteArray();
-                case RemoteStreamFailure failure: return SerializeRemoteStreamFailure(failure).ToByteArray();
-                case RemoteStreamCompleted completed: return SerializeRemoteStreamCompleted(completed).ToByteArray();
-                case SourceRefImpl sourceRef: return SerializeSourceRef(sourceRef).ToByteArray();
-                case SinkRefImpl sinkRef: return SerializeSinkRef(sinkRef).ToByteArray();
-                default: throw new ArgumentException($"Unsupported object of type {o.GetType()}", nameof(o));
-            }
+                SequencedOnNext onNext => SerializeSequencedOnNext(onNext).ToByteArray(),
+                CumulativeDemand demand => SerializeCumulativeDemand(demand).ToByteArray(),
+                OnSubscribeHandshake handshake => SerializeOnSubscribeHandshake(handshake).ToByteArray(),
+                RemoteStreamFailure failure => SerializeRemoteStreamFailure(failure).ToByteArray(),
+                RemoteStreamCompleted completed => SerializeRemoteStreamCompleted(completed).ToByteArray(),
+                SourceRefImpl sourceRef => SerializeSourceRef(sourceRef).ToByteArray(),
+                SinkRefImpl sinkRef => SerializeSinkRef(sinkRef).ToByteArray(),
+                _ => throw new ArgumentException($"Unsupported object of type {o.GetType()}", nameof(o))
+            };
         }
 
         public override object FromBinary(byte[] bytes, string manifest)
         {
-            switch (manifest)
+            return manifest switch
             {
-                case SequencedOnNextManifest: return DeserializeSequenceOnNext(bytes);
-                case CumulativeDemandManifest: return DeserializeCumulativeDemand(bytes);
-                case OnSubscribeHandshakeManifest: return DeserializeOnSubscribeHandshake(bytes);
-                case RemoteSinkFailureManifest: return DeserializeRemoteSinkFailure(bytes);
-                case RemoteSinkCompletedManifest: return DeserializeRemoteSinkCompleted(bytes);
-                case SourceRefManifest: return DeserializeSourceRef(bytes);
-                case SinkRefManifest: return DeserializeSinkRef(bytes);
-                default: throw new ArgumentException($"Unsupported manifest '{manifest}'", nameof(manifest));
-            }
+                SequencedOnNextManifest => DeserializeSequenceOnNext(bytes),
+                CumulativeDemandManifest => DeserializeCumulativeDemand(bytes),
+                OnSubscribeHandshakeManifest => DeserializeOnSubscribeHandshake(bytes),
+                RemoteSinkFailureManifest => DeserializeRemoteSinkFailure(bytes),
+                RemoteSinkCompletedManifest => DeserializeRemoteSinkCompleted(bytes),
+                SourceRefManifest => DeserializeSourceRef(bytes),
+                SinkRefManifest => DeserializeSinkRef(bytes),
+                _ => throw new ArgumentException($"Unsupported manifest '{manifest}'", nameof(manifest))
+            };
         }
 
         private SinkRefImpl DeserializeSinkRef(byte[] bytes)
@@ -129,7 +127,7 @@ private SequencedOnNext DeserializeSequenceOnNext(byte[] bytes)
         {
             var onNext = Proto.Msg.SequencedOnNext.Parser.ParseFrom(bytes);
             var p = onNext.Payload;
-            var payload = _serialization.Deserialize(
+            var payload = system.Serialization.Deserialize(
                 p.EnclosedMessage.ToByteArray(), 
                 p.SerializerId, 
                 p.MessageManifest?.ToStringUtf8());
@@ -169,7 +167,7 @@ private ByteString SerializeCumulativeDemand(CumulativeDemand demand) =>
         private ByteString SerializeSequencedOnNext(SequencedOnNext onNext)
         {
             var payload = onNext.Payload;
-            var serializer = _serialization.FindSerializerFor(payload);
+            var serializer = system.Serialization.FindSerializerFor(payload);
             var manifest = Akka.Serialization.Serialization.ManifestFor(serializer, payload);
 
             var p = new Payload