Fix bogus `DefaultFromField (Maybe NodeNodeCategory) instance`
Fixes #426 (closed).
@anoe This will restore the tree view for users after we have a team. The bug was I wrote a silly instance to deserialise the NodeNodeCategory
from a SQL value, and the lack of =<<
made the compiler auto-infer I was trying to deserialise an Int
and not a Maybe Int
, thus the error, yuck, sorry!