I couldn't make up my mind so two conflicting things are happening in bookmark.vm right now:
in #macro( showBookmarks $folderName $showFolderName $expandingFolder )
if the folder does not exist it simply prints $folderName (no error)
in #macro( showFolder $folder $showFolderName $expandingFolder )
if the folder contains no bookmarks than nothing is displayed (not even the $folder.name)
These should probably be more consistent, but I couldn't decide which was right: show an empty/non-existent folder or display nothing?