I did this to keep the original behavior of `categories`:

```ruby
self.categories = dir.downcase.split('/').reject { |x| x.empty? }
# ...
if self.categories.empty?
  self.categories = self.data.pluralized_array('category', 'categories').map {|c| c.to_s.downcase}
end
self.categories.flatten!
```

which is different from the one used for tags (that I also use for all classifications):

```ruby
self.tags = self.data.pluralized_array("tag", "tags").flatten
```

Having the same behavior for both would clean things up in my patch but I imagine the init, conditional assignation and `.to_s.downcase` are here for a good reason?

Yet I should probably rewrite this part in a `populate classifications` method.