Why does my FreeTTS code not work

Question

I wanted to convert text in a JTextArea into voice but I seem to keep getting an error at the same line.

Voice voice;
    VoiceManager vm = VoiceManager.getInstance();
    voice = vm.getVoice(VOICENAME);

    voice.allocate();
    try{
        voice.speak(voice_txt.getText());
    }
    catch (Exception e){
    JOptionPane.showMessageDialog(rootPane, e);}

This is the error I keep getting

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at FrameTextToSpeech.jButton1ActionPerformed(FrameTextToSpeech.java:75)

The error points to this line

voice.allocate();