I think we should later refactor this to use dependency injection. I.e. to have some sort of 'Null' pacemaker service, which defines these methods, but they return a 'no-op', a nil or empty array. Then, in the constructor, set the `@pacemaker` variable to an instance of either `NullPacemaker...` or `PacemakerServiceObject` and access it from these methods. That way, we won't have to repeatedly check if the service object is defined.