Remove database name necessity in uri connection schema

When I`m using URI connection schema without user and password, I get warnings from pymongo:
```
UserWarning: database name or authSource in URI is being ignored. If you wish to authenticate to ugc_development, you must provide a username and password.
  "must provide a username and password." % (db_name,))
```
So, why we can`t get database name from connect parameters if we don`t need auth on database?