I remember this bug was present when I was trying to upgrade from 4.x to 5.0. It prevented migration of all my projects to 5.0 as I use wildcard collections extensively. Then it got fixed at some point in 5.1 and I managed migrate from 4.x straight to 5.1. Now 5.2 has the same issue and it blocks the upgrade again. This bug is major for me. Still affects 5.2.12. Please take a look at this in the next release, the fix seems to be rather simple (adding a case for WildcardType in PluralAttributeMetadataImpl.getClassFromGenericArgument). Thank you.