Add net6.0 target framework

Author: AArnott

src/Microsoft.VisualStudio.Validation/Microsoft.VisualStudio.Validation.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
     <RootNamespace>Microsoft</RootNamespace>
 
     <Description>Common input validation and state verification utility methods.</Description>

src/Microsoft.VisualStudio.Validation/Requires.cs

@@ -446,7 +446,7 @@ public static void Argument([DoesNotReturnIf(false)] bool condition, string? par
         NotNull(resourceManager, nameof(resourceManager));
         if (!condition)
         {
-            throw new ArgumentException(Format(resourceManager.GetString(unformattedMessageResourceName, CultureInfo.CurrentCulture), arg1), parameterName);
+            throw new ArgumentException(Format(resourceManager.GetString(unformattedMessageResourceName, CultureInfo.CurrentCulture)!, arg1), parameterName);
         }
     }
 
@@ -463,7 +463,7 @@ public static void Argument([DoesNotReturnIf(false)] bool condition, string? par
         NotNull(resourceManager, nameof(resourceManager));
         if (!condition)
         {
-            throw new ArgumentException(Format(resourceManager.GetString(unformattedMessageResourceName, CultureInfo.CurrentCulture), arg1, arg2), parameterName);
+            throw new ArgumentException(Format(resourceManager.GetString(unformattedMessageResourceName, CultureInfo.CurrentCulture)!, arg1, arg2), parameterName);
         }
     }
 
@@ -479,7 +479,7 @@ public static void Argument([DoesNotReturnIf(false)] bool condition, string? par
         NotNull(resourceManager, nameof(resourceManager));
         if (!condition)
         {
-            throw new ArgumentException(Format(resourceManager.GetString(unformattedMessageResourceName, CultureInfo.CurrentCulture), args), parameterName);
+            throw new ArgumentException(Format(resourceManager.GetString(unformattedMessageResourceName, CultureInfo.CurrentCulture)!, args), parameterName);
         }
     }
 

src/Microsoft.VisualStudio.Validation/Verify.cs

@@ -101,7 +101,7 @@ public static void NotDisposed(IDisposableObservable disposedValue, string? mess
 
         if (disposedValue.IsDisposed)
         {
-            string objectName = disposedValue.GetType().FullName;
+            string objectName = disposedValue.GetType().FullName ?? string.Empty;
             if (message is object)
             {
                 throw new ObjectDisposedException(objectName, message);
@@ -121,7 +121,7 @@ public static void NotDisposed([DoesNotReturnIf(false)] bool condition, object?
     {
         if (!condition)
         {
-            string objectName = disposedValue is object ? disposedValue.GetType().FullName : string.Empty;
+            string objectName = disposedValue is object ? (disposedValue.GetType().FullName ?? string.Empty) : string.Empty;
             if (message is object)
             {
                 throw new ObjectDisposedException(objectName, message);