IMO, this is wrong. If there is no connection then we use the default connection. Or `default` is not always the default connection name. It depends of the user configuration. In the bundle we can rely on it as there is an alias service which use the `default `keyword to rely on the default connection but in the module this is not the case.

There is two way to fix that:
 * Gets the default connection name: `$defaultConnectionName = $sm->get('fridge.dbal')->getOptions()->getDefaultConnection()`
 * Gets the default connection: `$defaultConnection = $sm->get('fridge.dbal')->getDefaultConnection()`