BulkSaveChanges throws NullReferenceException when saving Many-to-many relationship

[SnakeBite94]

Hello,

when saving an entity with many-to-many relation to another entity (as described here), BulkSaveChanges throws an exception:

System.NullReferenceException: 'Object reference not set to an instance of an object.'
   at EFCore.BulkExtensions.DbContextBulkTransactionSaveChanges.<>c.<SaveChangesAsync>b__2_3(IEntityType e)
   at EFCore.BulkExtensions.DbContextBulkTransactionSaveChanges.<>c__DisplayClass2_0.<SaveChangesAsync>b__6(<>f__AnonymousType1`4 g)
   at Medallion.Collections.TopologicalSorter.TopologicalSort[TElement](ITopologicalSortProvider`1 provider)+MoveNext()
   at System.Collections.Generic.List`1.AddRange(IEnumerable`1 collection)
   at System.Linq.Enumerable.ConcatIterator`1.ToList()
   at EFCore.BulkExtensions.DbContextBulkTransactionSaveChanges.SaveChangesAsync(DbContext context, BulkConfig bulkConfig, Action`1 progress, Boolean isAsync, CancellationToken cancellationToken)
   at EFCore.BulkExtensions.DbContextBulkTransactionSaveChanges.SaveChanges(DbContext context, BulkConfig bulkConfig, Action`1 progress)
   at EFCore.BulkExtensions.DbContextBulkTransaction.Execute[T](DbContext context, Type type, IEnumerable`1 entities, OperationType operationType, BulkConfig bulkConfig, Action`1 progress)
   at EFCore.BulkExtensions.DbContextBulkExtensions.BulkSaveChanges(DbContext context, BulkConfig bulkConfig, Action`1 progress)
...

The code throwing the exception (private static async Task SaveChangesAsync(...))

There was a related, possibly same, but closed issue: 1311

We have a scaffolded model, the generated configuration looks like this:

entity.HasMany(d => d.TransportSubSystems)
     .WithMany(p => p.InterruptionAffectedDuties)
     .UsingEntity<Dictionary<string, object>>(
         "InterruptionAffectedDutySubsystem",
         l => l.HasOne<TransportSubSystem>().WithMany().HasForeignKey("SubSystemID").OnDelete(DeleteBehavior.ClientSetNull).HasConstraintName("FK_InterruptionAffectedDutySubsystems_SubSystemID"),
         r => r.HasOne<InterruptionAffectedDuty>().WithMany().HasForeignKey("InterruptionAffectedDutyID").HasConstraintName("FK_InterruptionAffectedDutySubsystems_InterruptionAffectedDuties"),
         j =>
         {
             j.HasKey("InterruptionAffectedDutyID", "SubSystemID");

             j.ToTable("InterruptionAffectedDutySubsystems", "Core");
         });

The UsingEntity<Dictionary<string, object>> is in accordance to the last "Important" note of the "Basic many-to-many" section on MSDN ). We use .net8 and EFCoreSqlServer 8.0.8.

The issue seems to be with the Dictionary used for the many-to-many relationship entity, because it does not have an EntityType for the toplogical sort.