Enable C# 8 nullable by default

Author: drewnoakes

src/Directory.Build.props

@@ -1,6 +1,13 @@
 <Project>
+
+  <PropertyGroup>
+    <LangVersion>8.0</LangVersion>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
   <!-- Workaround for https://github.com/dotnet/sourcelink/issues/572 -->
   <ItemGroup>
     <SourceRoot Include="$(MSBuildThisFileDirectory)/" />
   </ItemGroup>
+
 </Project>

src/NetMQ.Tests/EventDelegatorTests.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using Xunit;
 
 namespace NetMQ.Tests

src/NetMQ.Tests/ExceptionTests.cs

@@ -1,3 +1,5 @@
+#nullable disable
+
 #if !NETCOREAPP1_0
 
 using System.IO;

src/NetMQ.Tests/MsgTests.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using Xunit;
 
 namespace NetMQ.Tests

src/NetMQ.Tests/NetMQ.Tests.csproj

@@ -9,7 +9,6 @@
     <PackageTargetFallback Condition=" '$(TargetFramework)' == 'netcoreapp1.0' ">$(PackageTargetFallback);netcoreapp1.0;portable-net45+win8</PackageTargetFallback>
     <IsTestProject>true</IsTestProject>
     <TargetFrameworks>netcoreapp3.1;netcoreapp2.1;net47</TargetFrameworks>
-    <LangVersion>8</LangVersion>
   </PropertyGroup>
 
     <PropertyGroup>

src/NetMQ.Tests/OutgoingSocketExtensionsTests.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using Xunit;
 
 namespace NetMQ.Tests

src/NetMQ.Tests/ReceivingSocketExtensionsTests.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;

src/NetMQ.Tests/RequestWithRetryTests.cs

@@ -1,4 +1,6 @@
-#if !NET35
+#nullable disable
+
+#if !NET35
 using System;
 using System.Diagnostics;
 using NetMQ.Sockets;

src/NetMQ.Tests/SocketTests.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Net;

src/NetMQ.Tests/StreamTests.cs

@@ -1,4 +1,6 @@
-using Xunit;
+#nullable disable
+
+using Xunit;
 
 using NetMQ.Sockets;