Hi everyone, can anyone help please. I am using neatBeans 6.5.1 to learn how to develop web application. when run the application an error ocurred 'java.lang.NullPointerException' . Thanks alot

Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>

<head>
    <title>Murach's Java Servlets and JSP</title>
</head>

<body>
  <h1>Join our email list</h1>
  <p>To join our email list, enter your name and
     email address below. <br>
     Then, click on the Submit button.</p>

  <p><i>${message}</i></p>

  <form action="AddEmailToListServlet" method="get">
  <table cellspacing="5" border="0">
    <tr>
      <td align="right">First name:</td>
      <td><input type="text" name="firstName"
          value="${user.firstName}">
      </td>
    </tr>
    <tr>
      <td align="right">Last name:</td>
      <td><input type="text" name="lastName"
          value="${user.lastName}">
      </td>

    </tr>
    <tr>
      <td align="right">Email address:</td>
      <td><input type="text" name="emailAddress"
          value="${user.emailAddress}">
      </td>

    </tr>
    <tr>
      <td></td>
      <td><br><input type="submit" value="Submit"></td>
    </tr>
  </table>
  </form>
</body>

</html>