Issue with schemas when creating collections

[mvalencia-neostella]

Hi!

There's currently an issue with the create_collection(..) function in database.py. We recently ran into an issue in our production environment because we were creating a collection with a schema equal to an empty dictionary, i.e schema={}. Apparently, because of the way Arango works internally, this snowballed into a very weird issue where coordinators couldn't successfully update the collection but kept trying indefinitely. The Python function should also validate that the schema is not an empty dict. The issue was confirmed by Max and Kaveh in a support call

Thanks!