When trying to delete a class from the puppetclasses screen, this error is produced and the class is not deleted:

PGError
ERROR: update or delete on table "puppetclasses" violates foreign key constraint "environment_classes_puppetclass_id_fk" on table "environment_classes" DETAIL: Key (id)=(1312) is still referenced from table "environment_classes".
app/controllers/puppetclasses_controller.rb:41:in `destroy'
app/models/concerns/foreman/thread_session.rb:33:in `clear_thread'
lib/middleware/catch_json_parse_errors.rb:9:in `call'