Timer in MessageStream listener not initialized when heartbeat is turned off and throws NRE on Dispose

From end-user:

In MessageStreamListener.cs, there is a private member variable called timer (which is an instance of System.Threading.Timer). This is not initialized if HeartbeatSettings.IsEnabled is false. However the code will de-reference it two places within Heartbeat.Dispose() and one place within Heartbeat.Worker(). I saw that at a minimum it was throwing exceptions in Dispose() as a result of this.

I didn't see Worker() throw, but they do have a try/catch there, which if triggered by this would result in an erroneous "HB: Node not available" message being logged (I say erroneous because this particular exception would only happen if a read completed without an exception).