Null ref when attempting to back propagate non-existent results

[anpete]

Entity key is configured for IDENTITY but database is misconfigured to not have IDENTITY on the column.

Microsoft.Data.Entity.DbUpdateException: An error occurred while updating the entries. See the inner exception for details. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Data.Entity.ChangeTracking.Internal.Snapshot`2.set_Item(Int32 index, Object value)
   at Microsoft.Data.Entity.ChangeTracking.Internal.InternalEntityEntry.SetOriginalValue(IPropertyBase propertyBase, Object value)
   at Microsoft.Data.Entity.ChangeTracking.Internal.InternalEntityEntry.SetPropertyModified(IProperty property, Boolean isModified)
   at Microsoft.Data.Entity.ChangeTracking.Internal.ChangeDetector.PropertyChanged(InternalEntityEntry entry, IPropertyBase propertyBase)
   at Microsoft.Data.Entity.ChangeTracking.Internal.InternalEntityEntryNotifier.Dispatch(Action`1 action)
   at Microsoft.Data.Entity.Update.ModificationCommand.PropagateResults(ValueBuffer valueBuffer)
   at Microsoft.Data.Entity.Update.AffectedCountModificationCommandBatch.ConsumeResultSetWithPropagation(Int32 commandIndex, DbDataReader reader)
   at Microsoft.Data.Entity.Update.AffectedCountModificationCommandBatch.Consume(DbDataReader reader)
   --- End of inner exception stack trace ---
   at Microsoft.Data.Entity.Update.AffectedCountModificationCommandBatch.Consume(DbDataReader reader)
   at Microsoft.Data.Entity.Update.ReaderModificationCommandBatch.Execute(IRelationalConnection connection)
   at Microsoft.Data.Entity.Update.Internal.BatchExecutor.Execute(IEnumerable`1 commandBatches, IRelationalConnection connection)
   at Microsoft.Data.Entity.ChangeTracking.Internal.StateManager.SaveChanges(IReadOnlyList`1 entriesToSave)
   at Microsoft.Data.Entity.ChangeTracking.Internal.StateManager.SaveChanges(Boolean acceptAllChangesOnSuccess)
   at Microsoft.Data.Entity.DbContext.SaveChanges(Boolean acceptAllChangesOnSuccess)
   at Benchmarks.Data.ApplicationDbSeeder.Seed(ApplicationDbContext db) in C:\Dev\github\aspnet\benchmarks\src\Benchmarks\Data\ApplicationDbSeeder.cs:line 39