Nil assertion failed (NilAssertionError) when login to the AMI with wrong credentials

When trying to login AMI with incorrect credentials, expected to receive some `ConnectionError` but got `Unhandled exception: Nil assertion failed (NilAssertionError)`.

Detials:

```
from lib/asterisk/src/asterisk/ami/response.cr:29:20 in 'message'
from lib/asterisk/src/asterisk/ami.cr:88:15 in 'login'
```