In my case, I have traced the error to the service Microsoft Account Sign-in Assistant. In the Event Viewer, if you open the Details tab and expand System, you will see the PID associated with the event. Then look for that PID in Task Manager, Services tab. The service is manually triggered and stops after a brief period of time, so you have to search for the PID shortly after the event is logged or the service stops and the PID disappears. If you manually Start the service when it is Stopped, you can spawn the event and a new PID logged by the event will associate with the service.
So far, the only service I have seen associated with the event is the Microsoft Account Sign-in Assistant, so it seems to be the exclusive cause of the error. I have not been able to determine the Why? The PID keeps changing each time the service is restarted.
The service executable path is C:\WINDOWS\system32\svchost.exe -k netsvcs -p
The folders in the file path shown in the event log are not found within the file system on the machine. I believe the Null error in the event log is just identifying the instance where the service is making a call to a file path that does not exist. Why the service is making that call is likely a coding error that a user can't fix.