When a PrimaryOnlyService service exists on a replica set secondary, it will be in state kPaused. On a primary, it will be in state kRunning.

If one attempts to retrieve an instance while the service is in kPaused, the returned instance will be a boost::none.

OpObservers are run on both primaries and secondaries. This becomes an issue when attempting to run the ReshardingOpObserver, particularly here..

We should prepend a call to PrimaryOnlyService::isRunning() to verify that the PrimaryOnlyService is running before trying to retrieve the instance. Furthermore, we should check if the boost::optional is initialized and throw a DBException anyway, because attempting to index into an uninitialized boost::optional will create a segfault.