Null reference in relational composite key transformation when a key value doesn't exist

When using a relational composite key transformation on a field that doesn't always exist, a null reference exception is thrown:

Adapter import all entities for adapter failed.
Adapter import all entities for adapter 766401c6-e6e8-46d8-8c10-df86fbde0988 failed with reason Value cannot be null.
Parameter name: item. Duration: 00:00:04.5265410
Error details:
System.ArgumentNullException: Value cannot be null.
Parameter name: item
at Unify.Product.IdentityBroker.Repository.EntityLinqQueryExecutorInformation`1.AddValue(Guid searchGuid, TEntityKey keyValue, IValue item, Int32 columnSequence, Int32 valueSequence, IEntityCollectionKeyUtility`1 collectionKeyUtility)
at Unify.Product.IdentityBroker.Repository.EntityExpressionQueryVisitor`4.<>c_DisplayClass19.<>cDisplayClass1b.<CreateMultiValueRangeExpression>b_16(MultiKeyValue itemValue, Int32 itemValueIndex)
at Unify.Framework.Visitor.VisitT(IEnumerable`1 visitCollection, Action`2 visitor)
at Unify.Framework.Visitor.VisitT(IEnumerable`1 visitCollection, Action`2 visitor)
at Unify.Product.IdentityBroker.Repository.EntityExpressionQueryVisitor`4.CreateMultiValueRangeExpression(IMultiKey`1 multiKey, IEnumerable`1 sourceValueList, IQueryable`1 sourceQueryable)
at Unify.Product.IdentityBroker.Repository.VisitMethodWhereWithMultiValueEnumerableContains`4.Transform(MethodCallExpression expression)
at Unify.Product.IdentityBroker.Repository.EntityExpressionQueryVisitor`4.VisitMethodCall(MethodCallExpression m)
at Unify.Framework.ExpressionVisitorBase`11.Visit(Expression exp)
at Unify.Framework.Data.LinqContextConversionExpressionVisitorBase`5.ConvertExpression(Expression partitionExpression)
at Unify.Framework.Data.LinqQueryConversionProvider`5.GetOrderedQuery(Expression businessExpression, IQueryable`1 sourceQueryable, TContext sourceContext)
at Unify.Framework.Data.LinqWhereQuery`5.GetEnumerator()
at System.Linq.Lookup`2.CreateTSource(IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
at Unify.Product.IdentityBroker.EntityCompositeKeyDistinguishedNameStaticRelationValueAdapterBase.Transform(IEnumerable`1 sourceValue)
at System.Linq.Enumerable.AggregateTSource,TAccumulate(IEnumerable`1 source, TAccumulate seed, Func`3 func)
at System.Linq.Enumerable.<>c_DisplayClass12`3.<CombineSelectors>b_11(TSource x)
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at Unify.Framework.Collections.EnumerableExtensions.<ActionOnLast>d__17`1.MoveNext()
at System.Linq.Enumerable.<SelectManyIterator>d__14`2.MoveNext()
at Unify.Framework.Collections.EnumerableExtensions.<ActionOnLast>d__17`1.MoveNext()
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at Unify.Framework.Collections.ActionOnExceptionEnumerator`1.MoveNext()
at Unify.Framework.Collections.EnumerableExtensions.<ActionOnLast>d__17`1.MoveNext()
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Linq.Enumerable.<SelectManyIterator>d__14`2.MoveNext()
at System.Linq.Enumerable.<ConcatIterator>d__71`1.MoveNext()
at Unify.Framework.IO.LDIFComponentFileGenerator`1.GenerateFile(TextWriter writer, IEnumerable`1 entries)
at Unify.Product.IdentityBroker.LDIFAdapterBase.<>c_DisplayClass14`1.<CreateLDIFComponentStream>b_13(Stream stream)
at Unify.Framework.IO.LazyEvaluationStream.Evaluate(Object obj)

See attached configuration. The key fields are not always populated as a date relational transformation means position information is not populated for some users. Earlier tests of this transformation have succeeded with key fields from a connector, rather than further down the chain.