Yesterday and today, when deleting rejected files from my disk, I've received the following error: "an internal error occurred: ?:0: attempt to index a nil value." What's going on? This catalog seems OK, Lightroom CC Classic is working, but this is a new twist. What causes this, and what can I do to fix it? I'd rather not do anything that will destabilize my catalog, it's got 13 years of photos and data for a long term research project on harbor seals. Suggestions please!