removes fixme, adds comments and null checks

src/Umbraco.Core/ContentTypeBaseServiceProviderExtensions.cs

@@ -1,17 +1,16 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 using Umbraco.Core.Models;
 using Umbraco.Core.Services;
 
 namespace Umbraco.Core
 {
-    // fixme
-    public static class ContentTypeBaseServiceProviderExtensions
+    internal static class ContentTypeBaseServiceProviderExtensions
     {
+        //TODO: Maybe this should just be on the IContentTypeBaseServiceProvider interface?
         public static IContentTypeComposition GetContentTypeOf(this IContentTypeBaseServiceProvider serviceProvider, IContentBase contentBase)
-            => serviceProvider.For(contentBase).Get(contentBase.ContentTypeId);
+        {
+            if (contentBase == null) throw new ArgumentNullException(nameof(contentBase));
+            return serviceProvider.For(contentBase)?.Get(contentBase.ContentTypeId);
+        }
     }
 }

src/Umbraco.Core/Services/Implement/ContentTypeBaseServiceProvider.cs

@@ -18,6 +18,7 @@ namespace Umbraco.Core.Services.Implement
 
         public IContentTypeBaseService For(IContentBase contentBase)
         {
+            if (contentBase == null) throw new ArgumentNullException(nameof(contentBase));
             switch (contentBase)
             {
                 case IContent _:

src/Umbraco.Web/Macros/PublishedContentHashtableConverter.cs

@@ -199,8 +199,8 @@ namespace Umbraco.Web.Macros
                 Key = _inner.Key;
 
                 // TODO: ARGH! need to fix this - this is not good because it uses ApplicationContext.Current
-                CreatorName = _inner.GetCreatorProfile().Name;
-                WriterName = _inner.GetWriterProfile().Name;
+                CreatorName = _inner.GetCreatorProfile()?.Name;
+                WriterName = _inner.GetWriterProfile()?.Name;
 
                 var contentType = Current.Services.ContentTypeBaseServices.GetContentTypeOf(_inner);
                 ContentType = Current.PublishedContentTypeFactory.CreateContentType(contentType);