Error deleting navigation entry with page included.
https://sentry.io/via-j0/viaduct/issues/411385737/
AttributeError: 'NoneType' object has no attribute 'lstrip'
(2 additional frame(s) were not displayed)
...
File "app/views/navigation.py", line 136, in delete
path = entry.url.lstrip('/')
AttributeError: 'NoneType' object has no attribute 'lstrip'