A property value compatibility check can be triggered as an object graph is materialized during a query. The property it's complaining about could be on Closing, UserClosing, or even another type accessed via a navigation property on one of these types. The likely trigger is logic in an entity constructor - so check these; and also if you've overridden any UpdateNullEntity methods in your entities.
If neither of the above looks like the culprit, please send us your EDMX.