PR suggestions

Author: jonsequitur

src/System.CommandLine/Argument.cs

@@ -134,7 +134,7 @@ public override IEnumerable<CompletionItem> GetCompletions(CompletionContext con
 
         internal static Argument None { get; } = new NoArgument();
 
-        internal class NoArgument : Argument
+        private sealed class NoArgument : Argument
         {
             internal NoArgument() : base("@none")
             {

src/System.CommandLine/Argument{T}.cs

@@ -34,11 +34,9 @@ public Func<ArgumentResult, T>? DefaultValueFactory
             {
                 if (_defaultValueFactory is null)
                 {
-                    switch (this)
+                    if (this is Argument<bool> boolArgument)
                     {
-                        case Argument<bool> boolArgument:
-                            boolArgument.DefaultValueFactory = _ => false;
-                            break;
+                        boolArgument.DefaultValueFactory = _ => false;
                     }
                 }
                 return _defaultValueFactory;