describe-bindings-internal crashed on null keymap.
describe-bindings-internal crashed on null keymap.

This happens in the initial tmp buffer, making `describe-bindings` crash.  A simple check prints null bindings without flattening the null keymap.
cxxxr/lem,snmsts/lem,snmsts/lem,cxxxr/lem,cxxxr/lem,cxxxr/lem,snmsts/lem,snmsts/lem