RegisterRecord and TranslateColumn - MEDIAFILE and NODE types

I'm staging a custom table that acts as an XREF table using Media File and Tree Node IDs.

I followed the documentation using TranslationHelper.RegisterRecord and TranslationHelper.TranslateColumn but it's not clear what to use for the CodeName value for these types when registering for translation.

MediaFileInfo.TYPEINFO.CodeNameColumn and TreeNode.TYPEINFO.CodeNameColumn are both null so I'm not sure how it's supposed to look up the records on the target to do the translation.

Quick and dirty sample code I'm talking about (inside ColumnsTranslationEvents.RegisterRecords.Execute handler):

// Media file info
int fileID = ValidationHelper.GetInteger(e.Data.GetValue("FileID"), 0);
var info = MediaFileInfoProvider.GetMediaFileInfo(fileID);
var codeName = info.GetStringValue(MediaFileInfo.TYPEINFO.CodeNameColumn, string.Empty);
e.TranslationHelper.RegisterRecord(PredefinedObjectType.MEDIAFILE, fileID, codeName, 0);