There are a few problems in the binder that cause issues when mapping @Embeddable subtypes with discriminator-based inheritance when the root type extends from a @MappedSuperclass. See e.g. this comment (the Jira itself is unrelated).

Edit: the NPE in the original comment’s example mappings is caused by one class being annotated both @MappedSuperclass and @Embeddable at the same time. We decided to add explicit validation and error messages when an annotated class as more than one of the @Entity, @MappedSuperclass or @Embeddable annotations within this fix.