Okay this is an interesting one. The crash is one of my intentional fatal log messages to catch weirdness. The weirdness here is that the pregnancy system is trying to add bellyRating to your player character but it can't find any pregnancy in progress on you, implying something somewhere has gone wrong.
What's gone wrong is that the pregnancy is actually in Sera, but the code implementing the pregnancy process is just forcefully trying to call the changes on the PC. Which has a lot of implications regarding the entire Sera pregnancy process. I believe right now you'd also get log messages implying that the PC is pregnant, even though you're not, and there's likely other stat changes being applied to the PC inappropriately.
I have pinged The Preg Man for a discussion about what to do. I know what I think we should do to fix it, but DZ is better versed in how most of the pregnancies are actually implemented so rather than digging in and figuring out all of the specifics for myself I can just pick his brains before I pull the trigger.
