Ensure "dbname" is set in the uri, once again

Fixes #16625 (ref #10600)

python/plugins/db_manager/db_plugins/postgis/connector.py

@@ -56,7 +56,7 @@ def __init__(self, uri):
         password = uri.password() or os.environ.get('PGPASSWORD')
 
         # Do not get db and user names from the env if service is used
-        if uri.service() is None:
+        if not uri.service():
             if username is None:
                 username = os.environ.get('USER')
             self.dbname = uri.database() or os.environ.get('PGDATABASE') or username