Address all nullability warnings

Author: drewnoakes

src/NetMQ.Tests/InProcActors/AccountJSON/AccountActorTests.cs

@@ -19,6 +19,8 @@ public void AccountActorJsonSendReceiveTests()
 
                 var updatedAccount = JsonConvert.DeserializeObject<Account>(actor.ReceiveFrameString());
 
+                Assert.NotNull(updatedAccount);
+
                 Assert.Equal(10.0m, updatedAccount.Balance);
             }
         }

src/NetMQ.Tests/InProcActors/AccountJSON/AccountShimHandler.cs

@@ -53,6 +53,8 @@ public void Run(PairSocket shim)
 
                         string accountJson = msg[2].ConvertToString();
                         var account = JsonConvert.DeserializeObject<Account>(accountJson);
+                        Assumes.NotNull(accountAction);
+                        Assumes.NotNull(account);
                         AmendAccount(accountAction, account);
                         shim.SendFrame(JsonConvert.SerializeObject(account));
                     }

src/NetMQ/Core/Patterns/Utils/FairQueueing.cs

@@ -96,7 +96,7 @@ public void Activated(Pipe pipe)
 
         public bool Recv(ref Msg msg)
         {
-            return RecvPipe(ref msg, out Pipe _);
+            return RecvPipe(ref msg, out _);
         }
 
         public bool RecvPipe(ref Msg msg, [NotNullWhen(returnValue: true)] out Pipe? pipe)

src/NetMQ/Core/Patterns/Utils/LoadBalancer.cs

@@ -94,7 +94,7 @@ public void Activated(Pipe pipe)
 
         public bool Send(ref Msg msg)
         {
-            return SendPipe(ref msg, out Pipe _);
+            return SendPipe(ref msg, out _);
         }
 
         public bool SendPipe(ref Msg msg, out Pipe? pipe)

src/NetMQ/NetMQSocket.cs

@@ -472,12 +472,11 @@ internal int GetSocketOption(ZmqSocketOption option)
         /// <returns>an object of the given type, that is the value of that option</returns>
         /// <exception cref="TerminatingException">The socket has been stopped.</exception>
         /// <exception cref="ObjectDisposedException">This object is already disposed.</exception>
-        [return: MaybeNull]
-        internal T GetSocketOptionX<T>(ZmqSocketOption option)
+        internal T? GetSocketOptionX<T>(ZmqSocketOption option)
         {
             m_socketHandle.CheckDisposed();
 
-            return (T)m_socketHandle.GetSocketOptionX(option);
+            return (T?)m_socketHandle.GetSocketOptionX(option);
         }
 
         /// <summary>

src/NetMQ/ThreadSafeSocketOptions.cs

@@ -69,11 +69,10 @@ internal int GetSocketOption(ZmqSocketOption option)
         /// <returns>an object of the given type, that is the value of that option</returns>
         /// <exception cref="TerminatingException">The socket has been stopped.</exception>
         /// <exception cref="ObjectDisposedException">This object is already disposed.</exception>
-        [return: MaybeNull]
-        internal T GetSocketOptionX<T>(ZmqSocketOption option)
+        internal T? GetSocketOptionX<T>(ZmqSocketOption option)
         {
             m_socket.CheckDisposed();
-            return (T)m_socket.GetSocketOptionX(option);
+            return (T?)m_socket.GetSocketOptionX(option);
         }
 
         /// <summary>