[Stack Overflow #34730605, accepted answer, 13 votes]: Algolia cant facet-filter on null or empty-string values, facetFilters=author:null wont match. The workaround is to push a sentinel value at indexing time when the field is null (for example an explicit "none" token) and filter on that. Plan the sentinel in your indexing pipeline, not at query time.

Source context: Stack Overflow #34730605 (accepted answer, 13 votes): a developer asks how to facet-filter on records where a property is null or an empty string, like facetFilters=author:null. The accepted answer confirms Algolia doesnt support filtering on null or empty facet values, and gives the workaround: index a sentinel value when the field is null and filter on that instead.