Since updating my Adobe Lightroom Classic to the latest version (10.0 at the time of writing), I’ve been plagued by this error when adding to a collection or the quick collection
?:0: attempt to compare two nil values
Until Adobe issues an update to patch this, there are two actions you can take to workaround this error.
1. Optimise your catalog
Self explanatory – look for File > Optimize Catalog and wait a short while for your Lightroom catalog to be optimised. This worked for me for a couple of days, but the issue still returned. For a longer lasting workaround, move to step 2.
2. Sort your collection
Sorting your collection in any order other than custom will not trigger the error. To sort your collection, select the target collection (the collection where you want to save your image), and then look for View > Sort.
Choose any order other than custom, and you’ll once again be able to save to this collection without triggering an annoying error!