System.NullReferenceException at Orts.Simulation.Signalling.TrackCircuitSection.ClearSectionsOfTrainBehind, restore reports 'Invalid reservation for train')

[cjakeman]

First reported by Dan Reid at http://www.elvastower.com/forums/index.php?/topic/36334-open-rails-15-is-coming-soon/page__view__findpost__p__287973

Deatils are refined in later posts. Seems to be a brief time window of an activity during which Save files can be created which cannot be fully restored.

The Restore operation reports problems and then completes. In this case, the problem leads to fatal errors some minutes later, such as:

Error: System.NullReferenceException: Object reference not set to an instance of an object.
   at Orts.Simulation.Signalling.TrackCircuitSection.ClearSectionsOfTrainBehind(TrainRouted trainRouted, TrackCircuitSection startTCSectionIndex) in C:\Jenkins\jobs\Open Rails Stable\workspace\Source\Orts.Simulation\Simulation\Signalling\Signals.cs:line 7656