注册模块出错 新手求助 在线等

错误信息：
org.apache.jasper.JasperException: An exception occurred processing JSP page /adduser.jsp at line 1815: %> 
16:  
17: <% 
18:  String username = new String(request.getParameter("username").getBytes("ISO-8859-1")); 
19:  String password = new String(request.getParameter("password").getBytes("ISO-8859-1")); 
20:         String profession = new String(request.getParameter("profession").getBytes("ISO-8859-1")); 
21:  String email = new String(request.getParameter("email").getBytes("ISO-8859-1"));     
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:524)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:435)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
root cause java.lang.NullPointerException
org.apache.jsp.adduser_jsp._jspService(adduser_jsp.java:75)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
源码：
<%@page contentType="text/html;charset=gb2312"%> 
<%@page import="java.sql.*"%> 
<%! 
public static final String DBDRIVER = "com.microsoft.sqlserver.jdbc.SQLServerDriver"; 
public static final String DBURL = "jdbc:sqlserver://localhost:1433; DatabaseName = e_onlineroom"; 
public static final String DBUSER = "sa" ; 
public static final String DBPASS = "sa" ; 
 
%> 
<%   
Connection conn=null;//定义数据库连接对象 
Statement stmt=null;//定义结果集对象 
ResultSet rs=null ;//定义SQL对象结果集  
%> 
 
<% 
String username = new String(request.getParameter("username").getBytes("ISO-8859-1")); 
String password = new String(request.getParameter("password").getBytes("ISO-8859-1")); 
        String profession = new String(request.getParameter("profession").getBytes("ISO-8859-1")); 
String email = new String(request.getParameter("email").getBytes("ISO-8859-1"));     
%>  
 
<% 
//try 
//{ 
Class.forName(DBDRIVER) ; 
conn = DriverManager.getConnection(DBURL,DBUSER,DBPASS) ;//建立与数据库的连接 
            stmt=conn.createStatement();  
            String sql="select * from huiyuan where username='"+username+"'";         
rs=stmt.executeQuery(sql);  
if(rs.next()){
%>
    <script language="javascript">
     alert("此用户名已经存在，请重新注册！")
     history.back;
    </script>
<% 
}else{
String str = "INSERT INTO huiyuan VALUES('"+username+"','"+password+"','"+profession+"','"+email+"')";
stmt.executeUpdate(str);
%>
        <script language="javascript">
     alert("注册成功！")
    window.location.herf=("../login.jsp");
    </script>
<% 
}
rs.close();
stmt.close();
conn.close();