In the lesson_answers table the answer field can be NULL for end of branch, cluster and end of cluster pages.
This field can now be null.
Due to the version number changes in 1.8 and HEAD, some users will get this db fix twice (1.7 users who upgrade their 1.7 with this fix and then upgrade to 1.8 or later). Getting this fix twice does no harm as far as I can tell.
That's why we NEVER make database changes in stable branches ... you need to think about people going from stable to stable.
In this case I think you will get away with it but in future please avoid this sort of thing. Thanks!
Thanks for catching this one. This was very sloppy on my part because I somehow blindly rushed passed the Golden Rule of no database changes in stable branches. I'm really sorry about all this and it shouldn't happen again.
Cheers and thanks,