I've just read your post and the Stack Overflow link regarding NULL values and CI's ActiveRecord library.
The fact that it's a CI bug causes problems, as CI could fix it with any update.
Whilst if I was to patch a work around like the code you have provided yourself into the library, I would have to go through every other function within the library to ensure it also patches CI's bug.
Patching the library would then mean I would have to go through and test that every function within the library still works as intended.
Since I'm short of spare time at the moment, I will add this to my watch list, and if other users are encountering the same problem, I'll have a look into implementing it.