I also stumbled upon this scenario which seemed not to work with null values:

public class StringListEntity {
  @Id
  @GeneratedValue
  private Integer id;
  @ElementCollection
  @OrderColumn
  private List<String> values;
  // ...
}

@Test
public void testElementCollectionIndexedList() {
  doInJPA( this::entityManagerFactory, entityManager -> {
   final StringListEntity entity = new StringListEntity();
   entity.getValues().add( null );
   entity.getValues().add( "someValue" );
   entityManager.persist( entity );
  } );
}

In this use case, when the collection is persisted by ORM only the someValue element gets persisted; however when the list is hydrated from the database it will be [ null, "someValue" ] because of the indexing. Unfortunately Envers did not seem to adhere and work with such a use case. So I plan to mimic the behavior from PersistentList#readFrom where we expand the list in-flight as the results as added to guarantee space for the indexed use case.