Writing from input to text file

Question

I want to write person information from input to text file. My problem is that I always get NullPointerException. What could be wrong with this code? I have this method:

    public void skriveObjekt()throws IOException{

    try {

        RandomAccessFile randomAccessFile = new RandomAccessFile("bruker.txt", "rw");
        //randomAccessFile.defaultWriteObject();
        randomAccessFile.writeUTF(getFornavn());
        randomAccessFile.writeUTF(getEtternavn());
        randomAccessFile.writeUTF(getBrukernavn());
        randomAccessFile.writeUTF(getPassord());
        randomAccessFile.writeUTF(getAdresse());
        randomAccessFile.writeUTF(getEmail());
        randomAccessFile.writeChar(getFødselsdato().hashCode());

        FileHandler fileHandler = new FileHandler();
        fileHandler.lageFil();

        randomAccessFile.seek(200);

    } catch (IOException e) {
    e.printStackTrace();
}
}

Controller class

    @FXML
    private void LoggInn() throws IOException {
    FileHandler fileHandler = new FileHandler();
    fileHandler.lageFil();
    fileHandler.leseFil();
    Bruker bruker = null;

    bruker.skriveObjekt();
    }

I have this too but am unsure if it is right

void lageFil(){
    if(!file.exists()){
        file.mkdirs();
    }

}

File leseFil() throws IOException {

    try {
        FileReader fr = new FileReader( "brukere.txt");

        System.err.println("Filen finnes");
    }catch (FileNotFoundException fnfe){
        FileWriter fileWriter = new FileWriter( "brukere.txt");
        System.out.println("Filen er laget");
    }

    return null;
}