In my front matter I have:
--- layout: default title: "Services" top-navigation: order: 2 ---
top-navigation is only on some pages. Using liquid I want to filter all site pages which have a
top-navigation property and sort by
sort:'top-navigation.order' but that’s throwing an exception of
undefined method  for nil:NilClass.
How can I filter for pages that have
top-navigation and then sort?
Stack overflow post: https://stackoverflow.com/questions/45588558/liquid-filter-collection-where-not-null