Multivalue Group transform to a target entity with a NULL source field breaks reflection

Given this config:

and target connector data like this:

I am seeing reflection fail (no entities processed) with this error logged:

20220121,07:27:22,UNIFYBroker,Adapter,Error,"Request to reflect change entities of the adapter.
Request to reflect change entities of the SPOL Azure-mastered AD Groups (928e6c08-48d0-48da-8330-08ce0df4ef55) adapter errored with message: One or more errors occurred.. Duration: 00:00:01.4730403
Error details:
System.AggregateException: One or more errors occurred. ---> Unify.Framework.Collections.GroupedNameValueCollectionMissingFieldException: The entity does not contain a value for the onPremisesUserPrincipalName field.
   at Unify.Product.IdentityBroker.EntityBase`3.GetValueEntry(TKey key)
   at Unify.Product.IdentityBroker.RelationshipEntityProcessor.d__1.MoveNext()
   at System.Linq.Enumerable.d__17`2.MoveNext()
   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Unify.Product.IdentityBroker.SimpleValueMultivalueGroupTransformation.TransformItem(IEntity leftSideEntity, ILookup`2 rightSideLookup, IEntitySchemaFieldDefinition primaryKeyField)
   at System.Linq.Parallel.PartitionedDataSource`1.ListContiguousIndexRangeEnumerator.MoveNext(T& currentElement, Int32& currentKey)
   at System.Linq.Parallel.PipelineSpoolingTask`2.SpoolingWork()
   at System.Linq.Parallel.SpoolingTaskBase.Work()
   at System.Linq.Parallel.QueryTask.BaseWork(Object unused)
   at System.Threading.Tasks.Task.Execute()
   --- End of inner exception stack trace ---
   at System.Linq.Parallel.QueryTaskGroupState.QueryEnd(Boolean userInitiatedDispose)
   at System.Linq.Parallel.AsynchronousChannelMergeEnumerator`1.MoveNextSlowPath()
   at System.Linq.Parallel.QueryOpeningEnumerator`1.MoveNext()
   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at System.Linq.Enumerable.Aggregate[TSource,TAccumulate](IEnumerable`1 source, TAccumulate seed, Func`3 func)
   at Unify.Product.IdentityBroker.Adapter.ReflectChangePage(IChangesRegisterKey[] changedPage, IEntityPartitionContext connectorContext, IAdapterEntityPartitionUpdatableContext adapterContext, ITransformation transformation, DuplicateDnDetector duplicateDnDetector)
   at Unify.Product.IdentityBroker.Adapter.ReflectChangesInner()
   at Unify.Product.IdentityBroker.Adapter.ReflectChanges()
   at Unify.Product.IdentityBroker.AdapterAuditingDecorator.ReflectChanges()
   at Unify.Product.IdentityBroker.AdapterNotifierDecorator.ReflectChanges()
   at Unify.Product.IdentityBroker.ReflectAdapterOnChangeDueJob.RunOnAdapter(IOperationalAdapter adapter)
---> (Inner Exception #0) Unify.Framework.Collections.GroupedNameValueCollectionMissingFieldException: The entity does not contain a value for the onPremisesUserPrincipalName field.
   at Unify.Product.IdentityBroker.EntityBase`3.GetValueEntry(TKey key)
   at Unify.Product.IdentityBroker.RelationshipEntityProcessor.d__1.MoveNext()
   at System.Linq.Enumerable.d__17`2.MoveNext()
   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Unify.Product.IdentityBroker.SimpleValueMultivalueGroupTransformation.TransformItem(IEntity leftSideEntity, ILookup`2 rightSideLookup, IEntitySchemaFieldDefinition primaryKeyField)
   at System.Linq.Parallel.PartitionedDataSource`1.ListContiguousIndexRangeEnumerator.MoveNext(T& currentElement, Int32& currentKey)
   at System.Linq.Parallel.PipelineSpoolingTask`2.SpoolingWork()
   at System.Linq.Parallel.SpoolingTaskBase.Work()
   at System.Linq.Parallel.QueryTask.BaseWork(Object unused)
   at System.Threading.Tasks.Task.Execute()<---
---> (Inner Exception #1) Unify.Framework.Collections.GroupedNameValueCollectionMissingFieldException: The entity does not contain a value for the onPremisesUserPrincipalName field.
   at Unify.Product.IdentityBroker.EntityBase`3.GetValueEntry(TKey key)
   at Unify.Product.IdentityBroker.RelationshipEntityProcessor.d__1.MoveNext()
   at System.Linq.Enumerable.d__17`2.MoveNext()
   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Unify.Product.IdentityBroker.SimpleValueMultivalueGroupTransformation.TransformItem(IEntity leftSideEntity, ILookup`2 rightSideLookup, IEntitySchemaFieldDefinition primaryKeyField)
   at System.Linq.Parallel.PartitionedDataSource`1.ListContiguousIndexRangeEnumerator.MoveNext(T& currentElement, Int32& currentKey)
   at System.Linq.Parallel.PipelineSpoolingTask`2.SpoolingWork()
   at System.Linq.Parallel.SpoolingTaskBase.Work()
   at System.Linq.Parallel.QueryTask.BaseWork(Object unused)
   at System.Threading.Tasks.Task.Execute()<---
",Normal

In terms of correct functionality, since onPremisesUserPrincipalName is the Reference field I would expect a join to a target connector entity where the onPremisesUserPrincipalName value is NULL to be ignored (i.e. a NULL onPremisesUserPrincipalName value wouldn't be populated into MemberADUPNs).

Note: this ticket might be related to https://voice.unifysolutions.net/en/communities/6/topics/4082-foreign-multivalued-group-transformation-reports-value-cannot-be-null-for-multivalued-attribute but that one is a different transform and looks like a subtly different manifestation, so maybe not.