UMLR — InformationItem specified as a concrete Class, but it is abstract according to its constraint "not_instantiable"

On page 716, section 20.2.2 "InformationItem" (Classifier Description):

InformationItem is specified as a concrete Class, but in fact it is abstract according to its constraint "not_instantiable". Also, there are no concrete Classes in the UML which specialize InformationItem.

There is already the invariant constraint "convey_classifiers" included in InformationFlow; so why is InformationItem even necessary? If it is necessary, at least it should be defined as an abstract class – otherwise, it would need to have some kind of Element as an owner.