Hi Vlad,
the test you proposed doesn't test if the parentWithoutChild gets loaded and indeed it doesn't.

I added a assertEquals(2, result.size()); and it fails.

See the updated reproducer: https://github.com/schauder/issue-HHH-12999-superfluous-join/blob/master/src/test/java/org/hibernate/bugs/VladsTestCase.java