## Context
The validation throws after startTransaction() and outside the
surrounding try.
If the empty-enum branch ever fires, a BEGIN is left open on the
borrowed QueryRunner and never rolled back by this method the caller has
no way of knowing it now owes a ROLLBACK. Whatever the caller does next
on that QueryRunner runs inside the leftover transaction, and if its
lifecycle ends with a release() instead of a rollbackTransaction(), the
connection goes back to the pool with state still pending.
