@jwage: I'm worried about adding more constructor arguments here, since it's a change that then has to be implemented whenever we extend the class (to ensure we accept the argument with the same default value, and then pass it along to the parent). Assuming we allow both `$loggerCallable` and the QueryLogger to be optional (as I suggest [here](https://github.com/doctrine/mongodb/pull/153/files#r9897635))., what do you think about having setter methods for each? We'd naturally leave the `$loggerCallable` argument in place with a `null` default value for BC.