Make context nullable in IMessageContextAware

It's better for consumers with nullable reference types enabled

src/Abc.Zebus.Directory/Handlers/DirectoryCommandsHandler.cs

@@ -36,7 +36,7 @@ namespace Abc.Zebus.Directory.Handlers
             _blacklistedMachines = configuration.BlacklistedMachines.ToHashSet(StringComparer.OrdinalIgnoreCase);
         }
 
-        public MessageContext Context { get; set; } = default!;
+        public MessageContext? Context { get; set; }
 
         public void Handle(DecommissionPeerCommand message)
         {
@@ -45,7 +45,7 @@ namespace Abc.Zebus.Directory.Handlers
 
         public void Handle(RegisterPeerCommand message)
         {
-            if (_blacklistedMachines.Contains(Context.Originator.SenderMachineName!))
+            if (_blacklistedMachines.Contains(Context!.Originator.SenderMachineName!))
                 throw new InvalidOperationException($"Peer {Context.SenderId} on host {Context.Originator.SenderMachineName} is not allowed to register on this directory");
 
             var peerTimestampUtc = message.Peer.TimestampUtc;

src/Abc.Zebus.Persistence/Handlers/MessageHandledHandler.cs

@@ -19,14 +19,14 @@ namespace Abc.Zebus.Persistence.Handlers
             _configuration = configuration;
         }
 
-        public MessageContext Context { get; set; } = default!;
+        public MessageContext? Context { get; set; }
 
         public void Handle(MessageHandled message)
         {
-            if (_configuration.PeerIdsToInvestigate != null && _configuration.PeerIdsToInvestigate.Contains(Context.SenderId.ToString()))
+            if (_configuration.PeerIdsToInvestigate != null && _configuration.PeerIdsToInvestigate.Contains(Context!.SenderId.ToString()))
                 _log.Info($"Ack received from peer {Context.SenderId}. MessageId: {message.MessageId}");
 
-            _inMemoryMessageMatcher.EnqueueAck(Context.SenderId, message.MessageId);
+            _inMemoryMessageMatcher.EnqueueAck(Context!.SenderId, message.MessageId);
 
             var activeMessageReplayer = _messageReplayerRepository.GetActiveMessageReplayer(Context.SenderId);
             activeMessageReplayer?.Handle(message);

src/Abc.Zebus.Persistence/Handlers/StartMessageReplayCommandHandler.cs

@@ -9,11 +9,11 @@
             _messageReplayerRepository = messageReplayerRepository;
         }
 
-        public MessageContext Context { get; set; } = default!;
+        public MessageContext? Context { get; set; }
 
         public void Handle(StartMessageReplayCommand message)
         {
-            var peer = Context.GetSender();
+            var peer = Context!.GetSender();
 
             var currentMessageReplayer = _messageReplayerRepository.GetActiveMessageReplayer(peer.Id);
             currentMessageReplayer?.Cancel();

src/Abc.Zebus/IMessageContextAware.cs

@@ -2,6 +2,6 @@
 {
     public interface IMessageContextAware
     {
-        MessageContext Context { get; set; } 
+        MessageContext? Context { get; set; }
     }
-}
+}