I've just upgraded Spring Boot, which upgraded Hibernate ORM from 5.4.12.Final to 5.4.18.Final

I have an association

    @javax.persistence.ManyToOne(fetch = FetchType.LAZY)
    @javax.validation.constraints.NotNull
    private Product product;

I have logic that inspects metadata and collects nullable associations of an entity

List<Attribute<?, ?>> fields = new ArrayList<>();

fields.addAll(entityType.getSingularAttributes().stream()
    .filter(singularAttribute -> singularAttribute.isAssociation()
        && singularAttribute.getType() instanceof EntityType
        && singularAttribute.isOptional())
    .collect(Collectors.toList()));

return fields;

where `entityType` is `javax.persistence.metamodel.EntityType`

Previously, the `isOptional` honoured the `NotNull` constraint and returned false, not it returns true which breaks my logic. I'm not yet sure if this is a miss-configuration by Spring Boot or by my application or if it's a bug in Hibernate, but with the upgrade this changed unexpectedly.