You can set a breakpoint at AbstractLoadPlanBuildingAssociationVisitationStrategy Line #669 to narrow down the entity and the field. Maybe the one-to-many collection involve some class which is not specified as entity. Definitively a coding imperfection for the javadoc of {{org.hibernate.loader.plan.spi.FetchSource#resolveEntityReference()}}has said null value could be returned.

Your persistence.xml seems not very helpful to narrow down the root cause, though, at least for someone who is not using JBoss product.