Workarounds for null dereference bugs

[carolhanna01]

I've encountered some null dereference issues while running some longer experiments. I added some null safety checks that prevent the search from prematurely terminating due to the null exceptions that get thrown. These are not root-cause fixes, just workarounds that enabled us to run the search to completion. I hope that this can help pinpoint the underlying issues!

[clegoues]

Hi Carol! Sorry for the slow handling of these, ha. I'm inclined to just accept these, but I'm wondering if you did any digging into why any of these things MIGHT return null? Or if there's example code you have where you know it happens?