Fix when categories or tags are empty

[millerf]

Return [] if categories return empty. See #28602

Proposed changes:

• Return [] if categories return empty. See

Testing instructions:

See #28483

Does this pull request change what data or activity we track or use?

no

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[artpi]

Works!

[n3f]

Looks good to me and solves the issue in #28604. (I do have a comment about the correctness of the existing logic though)