mongod running with --auth parameter

Connecting without user/password parameters throws a non-speaking
error message. A proper error message would "no authentication credentials provided"
instead of:

ajung@blackmoon:~/sandboxes/occ> bin/mongodump -h b --port 10200 -d foo
connected to: b:10200
DATABASE: foo to dump/foo
terminate called after throwing an instance of 'std::out_of_range'
what(): basic_string::substr
Aborted