Make it clear that logging levels can be None.
Make it clear that logging levels can be None.

neiljerram/felix,matthewdupre/felix,alexhersh/calico,TrimBiggs/calico,Metaswitch/calico,TrimBiggs/calico,Metaswitch/calico,neiljerram/felix,matthewdupre/felix,alexhersh/calico,neiljerram/felix,neiljerram/felix