Extending entity unfetched attribute

I have an entity [Network] which extends [Organisation]

In [Organisation] I have an array list of [Contacts].

When I try to to create a new contact and set the organisation to a [Network] I get an error saying

"IllegalStateException: Cannot get unfetched attribute [networkParticipantIdentifier] 
from detached object com.daryn.entity.Network-966cefa5-bc6e-b0c9-e6f1-"

I don’t know why it needs to load the unfetched attributes anyway…

Actually I have figured it out from here:

Entity extension is actually designed for extending entities belonging to application components. There is no need to use this mechanism for entities belonging to one project - use normal inheritance as described here.

Regarding your problem with the “Cannot get unfetched attribute” exception, please provide the source code of the entities and how you create/load them. Or better reproduce on a test project.