public boolean allowsUnlock(UUID ownerId) {
        Preconditions.checkNotNull(ownerId);
        return ownerId.equals(lockOwnerId);
    }
@Test(expected = NullPointerException.class)
    public void testAllowsUnlock_nullTransactionId() {
        LockGuard stateLock = LockGuard.NOT_LOCKED;
        stateLock.allowsUnlock(null);
    }