Trying to send package through socket on a timer; getting an exception on the thread

Question

I'm trying to send a variable to another java application every 5 seconds, but I'm getting "Exception in thread "Timer-0" java.lang.NullPointerException" and I can't figure out which part is messing up.

Timer/main:

    SendCommunication sendComm = new SendCommunication();
    sendComm.init("localhost", 8081);

    Timer timer = new Timer();
    timer.schedule(new TimerTask() {
        @Override public void run() {
            sendComm.packData();
            sendComm.sendPackage();
        }
    }, 0L, 5000L);

packData:

public void packData() {

    DatabaseOperation dbOperation = DatabaseOperation.getInstance();
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream( );

    String tempGroupDist = Integer.toString(dbOperation.getGroupDistance());

    try {
        outputStream.write(tempGroupDist.getBytes());
        this.sendData = outputStream.toByteArray();
    }
    catch (IOException ex) {
        ex.printStackTrace();
    }
}

sendPackage:

public void sendPackage() {
    try {
        System.out.println("Sending data to " + this.sendData.length + " bytes to server.");
        DatagramPacket sendPacket = new DatagramPacket(this.sendData, this.sendData.length, this.ipAddress, this.serverPort);
        this.clientSocket.send(sendPacket);

        DatagramPacket receivePacket = new DatagramPacket(this.receiveData, this.receiveData.length);

        System.out.println ("Waiting for return packet");
        this.clientSocket.setSoTimeout(10000);

        try {
            this.clientSocket.receive(receivePacket);
            String modifiedSentence = new String(receivePacket.getData());

            InetAddress returnIPAddress = receivePacket.getAddress();

            int port = receivePacket.getPort();

            System.out.println ("From server at: " + returnIPAddress + ":" + port);
            System.out.println("Message: " + modifiedSentence);

        }
        catch (SocketTimeoutException ste) {
            System.out.println ("Timeout Occurred: Packet assumed lost");
        }

        this.clientSocket.close();
    }
    catch (IOException ex) {
        ex.printStackTrace();
    }
}

getGroupDistance:

    public int getGroupDistance() {
    try {
        sqd = con.prepareStatement("SELECT SUM(DISTANCE) FROM Patients");
        rs = sqd.executeQuery();
        if (rs.next()) {
            int sum = rs.getInt(1);
            if (groupDistance == 0) {
                this.groupDistance = sum;
            } else {
                this.groupDistance = this.groupDistance + sum;
            }

            sqd.close(); // lukker statemenet
            stmt.close();
            rs.close(); // lukker resultSet

            stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
            String sql = "SELECT * FROM Patients";
            rs = stmt.executeQuery(sql);

            rs.next();

        }

    } catch (SQLException bananFisk) {
        bananFisk.printStackTrace();
    }
    return groupDistance;
}

My confusion stem from the following: packData + sendPackage work on their own. getGroupDistance works on its own. I'm using an identical timer somewhere else in the code and that works fine.

This combination however doesn't work and I can't figure out why..

EDIT: I fixed it even though I still don't know what the problem was. But if I move the timer to the initialization it runs fine and I get the expected result. The link to the NullPointerException might hold the answer to why it didn't work before but I couldn't seem to find the error, seeing as all elements worked on their own.