So the issue is with Javassist 3.22 which does not support JDK 11. That's why you have this exception, if you have the same one as Fabio.

Frankly, the Spring Boot version you are using is not really suitable for JDK 11.

The next version of Spring Boot should come with ORM 5.3 which supports JDK 11. You can maybe try to upgrade to it by setting the right property to a 5.3 version but I'm not sure it will work very well.

If this error is the only one you have, you can probably fix it by upgrading Javassist to 3.23 but we didn't test 5.2 with JDK 11 so I can't guarantee you won't have any other problem.

Fabio tested forcing the Javassist version and at least your project works with that.