conexão no ldap, me ajudem

Programação Java
#1

Estou com o seguinte problema,estou querendo cadastrar um usuario novo com esse codigo abaixo:

class ADDTEL {

private DirContext ctx = null;
  private String filter = "(&(sn=*)(cn=<%USERNAME%>))";
  private String usersCtx = "o=triscal";
  private String providerURL = "ldap://192.168.1.37:389/";
  private String usernameAttribute = "cn";
  private String phoneAttribute = "telephonenumber";
  private String mobileAttribute = "mobile";
  private String homePhoneAttribute = "homephone";
  private String uidAttribute = "uid";
  private String username = "CN=domadmin,o=triscal";
  private String password = "M@nager";


  private InitialDirContext ldapBind() throws NamingException {
    
    ctx = ldapBind();     
    Hashtable env = new Hashtable();
    env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.ldap.LdapCtxFactory");
    env.put(Context.PROVIDER_URL, providerURL);
    if (username!=null){
      env.put(Context.SECURITY_PRINCIPAL, username);
    }
    if (password!=null){
      env.put(Context.SECURITY_CREDENTIALS, password);
    }
    return new InitialDirContext(env);
  }

  public void addUsers(String user, String res, String com, String cel) throws Exception, NamingException{
    ModificationItem[] mods = new ModificationItem[4];

                 
            mods[0] = new ModificationItem(DirContext.ADD_ATTRIBUTE,
                new BasicAttribute("cn", user));
          
            mods[1] = new ModificationItem(DirContext.ADD_ATTRIBUTE,
                new BasicAttribute("homephone", res));
    
            mods[2] = new ModificationItem(DirContext.ADD_ATTRIBUTE,
                new BasicAttribute("telephonenumber", com));

            mods[3] = new ModificationItem(DirContext.ADD_ATTRIBUTE, 
                new BasicAttribute("mobile", cel));

            String userDN = usernameAttribute + "=" + user + "," + usersCtx;
            ctx.modifyAttributes(userDN, mods);
  }

 public static void main(String[] args) throws Exception{
  
    ADDTEL l = new ADDTEL();

    l.addUsers("Aliche","23 2576-4629","76 2555-2550","21 9999-8771");


  }

e esta ocorrendo o seguinte erro em ctx.modifyAttributes(userDN, mods);

Exception in thread “main” java.lang.NullPointerException
at triscal.com.br.ADDTEL.addUsers(ADDTEL.java:72)
at triscal.com.br.ADDTEL.main(ADDTEL.java:79)

alguem pode me ajudar?!
obrigado
andré

#2