Object reference during NServiceBus start up.

One of our NServiceBus services started getting this error today.

Fatal    System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Object.GetType()
   at NServiceBus.Timeout.Core.TimeoutRunner.CacheExistingTimeouts()
   at NServiceBus.Timeout.Core.TimeoutRunner.Run()
   at System.Collections.Generic.List`1.ForEach(Action`1 action)
   at NServiceBus.Unicast.UnicastBus.NServiceBus.IStartableBus.Start(Action startupAction)
   at NServiceBus.Hosting.GenericHost.Start() in c:\TeamCity\buildAgent\work\nsb.master_8\src\hosting\NServiceBus.Hosting\GenericHost.cs:line 34

Turns out the NServiceBus.Persistence connection string was pointing to a Raven instance that was turned off.