Users are very likely to get this error, so we should make sure it's clear and guides the user to a solution.
We should make the message clearer and mention the various solutions:
Define the non-owning side of the association in the target entity (when using Hibernate ORM)
OR define the inverse side of the association using @AssociationInverseSide
OR (expert feature) disable automatic reindexing when the target entity changes using @IndexingDependency(reindexOnUpdate = ReindexOnUpdate.NO)