Sorry about this, in my haste to copy and paste from the old addon, I missed an important part of code - yikes!
So this update fixes that (basically if you posted an article with no prefix at all it would fail)
As a bonus though and to say sorry about that, I've integrated another one of my addons into it.
Navigation Block Prefixes
If you enable this feature, the item assigned prefixes will appear in the navigation block, underneath the relevant category where the child categories go.
In this example "Ford Cars" is the real category, whereas "Fiesta", "Puma" and "Ranger" are just links to show only those prefixes in the "Ford Cars" category.
You can choose how they are sorted (or to turn them off entirely) in the admin option:
: As this works from cache which is updated when an article is added/edited - you'll need to edit an existing article and switch the prefix to something else then back again to build it the first time around. After this it will update automatically
Yes I could have put that code in a repository and run on install, but I was tired ok!