boolean dropSession(final String clientId, boolean removeSessionState) {
        LOG.debug("Disconnecting client: {}", clientId);
        if (clientId == null) {
            return false;
        }

        final Session client = pool.get(clientId);
        if (client == null) {
            LOG.debug("Client {} not found, nothing disconnected", clientId);
            return false;
        }

        client.closeImmediately();
        if (removeSessionState) {
            purgeSessionState(client);
        }

       LOG.debug("Client {} successfully disconnected from broker", clientId);
       return true;
    }
@Test
    public void testDropSessionWithNullClientId() {
        assertFalse(sut.dropSession(null, ANY_BOOLEAN), "Can't be successful when null clientId is passed");
    }