Better error handling

Upsilon/BaseTypes/UserData/ListUserData.cs

@@ -64,7 +64,7 @@ namespace Upsilon.BaseTypes.UserData
             }
             else
             {
-                throw new ScriptRuntimeException(
+                throw new ScriptRuntimeException(null,
                     $"Tried indexing a CSharp list with a value that's not an integer. Value: {scriptIndex.ToCSharpObject()}",
                     span, diagnostics.ScriptString.GetSpan(span));
             }