FilterRemoveNullValues change in CMS 5
In CMS 4 for the filter to remove a page the property specified had to exist on the page being filtered as well as the value being null.
In CMS 5 this has changed so the filter always assumes that the property always exist and only checks if the property value is null.
I guess that’s not wrong but depending on the circumstances I can see a possibility that you have a mixed page data collection from different sources where you just want to do the filtering on only the pages that have this particular property and just ignore the rest.
In my case we hade some old code that used this filter and still returned pages due to the property exist check. But after migrating to CMS 5 all pages got filtered out.