categories by size (descending) not working

[paul-hammant]

I'm doing something wrong, obviously, but the following doesn't work:

jekyll_sort:
src: categories_list
direction: down
by: size
dest: categories_list_by_size

Specifically, when categories_list_by_size is used in a for-loop, that loop is empty. 'size' is the property that says now many there are in that category.