Null OutputStream

package testeserial;

import javax.comm.*;
import java.io.*;
import java.awt.TextArea;
import java.awt.event.*;
import java.util.TooManyListenersException;

/**
     * A class to handle <code>KeyEvent</code>s generated by the messageAreaOut.
     * When a <code>KeyEvent</code> occurs the <code>char</code> that is
     * generated by the event is read, converted to an <code>int</code> and
     * writen to the <code>OutputStream</code> for the port.
     */
    class KeyHandler extends KeyAdapter {
        private static KeyHandler INSTANCE;
    private static Entrada_Saida es;

    /**
     * Creates the KeyHandler.
     * @param os The OutputStream for the port.
     */
    private KeyHandler() {}
       
        public void setES(Entrada_Saida es) {
        this.getInstance().es = es.getInstance();
    }
       
        public Entrada_Saida getES() {
            return this.getInstance().es;
        }

        public void setValor(int valor) {
            String strValor = Integer.toString(valor);
            byte[] bytes = strValor.getBytes();
            try {
                this.getInstance().getES().getInstance().getOS().write(bytes); // NESTA LINHA!
            } catch (IOException e) {}

        }
       
    public void keyTyped(KeyEvent evt) {
        char newCharacter = evt.getKeyChar();

            if (es == null) {
                es = es.getInstance();
            }
           
        try {
        es.getInstance().getOS().write((int) newCharacter);
        } catch (IOException e) {
        System.err.println("OutputStream write error: " + e);
        }
        }
       
        public static KeyHandler getInstance() {
            if (INSTANCE == null) {
                INSTANCE = new KeyHandler();
            }
            return INSTANCE;
        }
    }

/*
 * Entrada_Saida.java
 *
 * Created on 31 de Maio de 2007, 17:55
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 */

package testeserial;

import javax.comm.*;
import java.io.*;
import java.awt.TextArea;
import java.awt.event.*;
import java.util.TooManyListenersException;

public class Entrada_Saida {
    private static Entrada_Saida INSTANCE;
    private OutputStream os;
    private InputStream is;
   
    /** Creates a new instance of Entrada_Saida */
    private Entrada_Saida() {}
   
    public void setOS(OutputStream os) {
        this.getInstance().os = os;
    }
   
    public OutputStream getOS() {
        return this.getInstance().os;
    }
   
    public void setIS(InputStream is) {
        this.getInstance().is = is;
    }
   
    public InputStream getIS() {
        return is;
    }
   
    public static Entrada_Saida getInstance() {
        if (INSTANCE == null) {
            INSTANCE = new Entrada_Saida();
        }
        return INSTANCE;
    }
   
}