If a frontend for some reason tries to unsubscribe from a non existing subscription, the following error is logged:

Could not execute command from ({"command"=>"unsubscribe", "identifier"=>"{\"channel\":\"SomeChannel\"}"}) [NoMethodError - undefined method `unsubscribe_from_channel' for nil:NilClass]

Instead, it will now properly log:

Could not execute command from ({"command"=>"unsubscribe", "identifier"=>"{\"channel\":\"SomeChannel\"}"}) [RuntimeError - Unable to find subscription with identifier: {"channel":"SomeChannel"}]