#fixed code
                                public void close(IotHubConnectionStatusChangeReason reason, Throwable cause) throws DeviceClientException
    {
        if (reason == null)
        {
            //Codes_SRS_IOTHUBTRANSPORT_34_026: [If the supplied reason is null, this function shall throw an
            // IllegalArgumentException.]
            throw new IllegalArgumentException("reason cannot be null");
        }

        this.cancelPendingPackets();

        //Codes_SRS_IOTHUBTRANSPORT_34_023: [This function shall invoke all callbacks.]
        this.invokeCallbacks();

        if (this.taskScheduler != null)
        {
            this.taskScheduler.shutdown();
        }

        if (this.scheduledExecutorService != null)
        {
            this.scheduledExecutorService.shutdownNow();
            this.scheduledExecutorService = null;
        }

        //Codes_SRS_IOTHUBTRANSPORT_34_024: [This function shall close the connection.]
        if (this.iotHubTransportConnection != null)
        {
            this.iotHubTransportConnection.close();
        }

        //Codes_SRS_IOTHUBTRANSPORT_34_025: [This function shall invoke updateStatus with status DISCONNECTED and the
        // supplied reason and cause.]
        this.updateStatus(IotHubConnectionStatus.DISCONNECTED, reason, cause);

        // Notify send thread to finish up so it doesn't survive this close
        synchronized (this.sendThreadLock)
        {
            this.sendThreadLock.notifyAll();
        }

        // Notify receive thread to finish up so it doesn't survive this close
        synchronized (this.receiveThreadLock)
        {
            this.receiveThreadLock.notifyAll();
        }

        log.info("Client connection closed successfully");
    }
#vulnerable code 
                                public void close(IotHubConnectionStatusChangeReason reason, Throwable cause) throws DeviceClientException
    {
        if (reason == null)
        {
            //Codes_SRS_IOTHUBTRANSPORT_34_026: [If the supplied reason is null, this function shall throw an
            // IllegalArgumentException.]
            throw new IllegalArgumentException("reason cannot be null");
        }

        this.cancelPendingPackets();

        //Codes_SRS_IOTHUBTRANSPORT_34_023: [This function shall invoke all callbacks.]
        this.invokeCallbacks();

        if (this.taskScheduler != null)
        {
            this.taskScheduler.shutdown();
        }

        if (this.scheduledExecutorService != null)
        {
            this.scheduledExecutorService.shutdownNow();
            this.scheduledExecutorService = null;
        }

        //Codes_SRS_IOTHUBTRANSPORT_34_024: [This function shall close the connection.]
        if (this.iotHubTransportConnection != null)
        {
            this.iotHubTransportConnection.close();
        }

        //Codes_SRS_IOTHUBTRANSPORT_34_025: [This function shall invoke updateStatus with status DISCONNECTED and the
        // supplied reason and cause.]
        this.updateStatus(IotHubConnectionStatus.DISCONNECTED, reason, cause);

        log.info("Client connection closed successfully");
    } 
                            #location 34 
                            #vulnerability type THREAD_SAFETY_VIOLATION