Use named argument when passing null

src/Compilers/Core/MSBuildTask/CommandLineBuilderExtension.cs

@@ -146,7 +146,7 @@ internal void AppendSwitchIfNotNull
             string[] attributes
         )
         {
-            AppendSwitchIfNotNull(switchName, parameters, attributes, null /* treatAsFlag */);
+            AppendSwitchIfNotNull(switchName, parameters, attributes, treatAsFlags: null);
         }
 
         /// <summary>

src/Compilers/Core/MSBuildTask/ManagedCompiler.cs

@@ -954,7 +954,7 @@ protected override bool ValidateParameters()
         /// </summary>
         internal static bool ListHasNoDuplicateItems(ITaskItem[] itemList, string parameterName, TaskLoggingHelper log)
         {
-            return ListHasNoDuplicateItems(itemList, parameterName, null, log);
+            return ListHasNoDuplicateItems(itemList, parameterName, disambiguatingMetadataName: null, log);
         }
 
         /// <summary>