This error was happening entirely because of my fault.
We generate all of our models, interfaces/abstract classes/entities and the required hibernate/JPA annotations from GraphQL.
In a few cases a composite is used as a primary key and in two places the generated code had a bug where an @Embeddable's field referred to an interface instead of one of the generated sub-types.
Fixing that on our side does away with this error, however the error message is not at all indicative of the cause (maybe it's something you'd know if you're a seasons hibernate dev. but this is our first Hibernate/OGM encounter so it took some digging in the sources to work out what was going on).
In effect, I'm raising this ticket, not as a bug but as an improvement request.
I was trying to reproduce this with a test case but have struggled to run the tests. The extensions to the model that "should" reproduce this is:
It's incomplete since I wasn't able to run the tests but I've attached a patch of what I was trying to do to reproduce and if it had worked would've changed cache initializer.
(incomplete reproducer attempt, feel free to ignore)
This affects current master.
This was "introduced" by the fixes in https://github.com/hibernate/hibernate-ogm-ignite/pull/18/