They raised KeyError before. I'm changing this because the code uses
hasattr() to check for the presence of a key. This worked accidentally
before, because hasattr() silences all exceptions in python 2. However,
in python3, this isn't the case anymore.
I had a look around to see if anything depended on this raising a
KeyError and I couldn't find anything. Of course, I could have simply
missed it.
Signed-off-by: Adrian Tschira <nota@notafile.com>