I was playing around on SEDE when I noticed some questions have a favourite count of 0, while the majority have a favourite count of
NULL. What's the reason behind this? For the questions with a count of 0, did somebody add it as a favourite in the past and removed it later (possibly even when their account was removed)? Looking at this answer, it might very well be the case.
This behaviour seems to happen on all sites in the network, not just Meta. I've already checked migrations as a possible cause, but nope. Here are two queries to view more examples:
A related issue is Why do some comments have 0 score but others have null score in Data Explorer?. While this behaviour makes writing some niche queries slightly more complex than needed, it's far from being a bug and this question is also to satisfy my curiosity.