mailCheck里检查username和pasword输入是否为空，如果为空则请求转发到maillogin.jsp中，但是结果没有跳转，请问是什么原因？

用debug调试有跳转，但是会报错。
maillogin.jsp:
<body>
<p>欢迎光临邮件系统</p>
<p>Session ID：<%=session.getId() %></p>
<%
String name = null;
String password = null;
if(!session.isNew()){
name =(String)session.getAttribute("username");
password =(String)session.getAttribute("password");
}else{
response.getWriter().print("新的会话");
name = "";
password = "";
}

%>
<form action="mailcheck.jsp" method="POST">
姓名：<input type="text" name="username" value="<%=name %>"/><br>
密码：<input type="password" name="password" value="<%=password %>" /><br>
<input type="submit" value="登陆">
</form>
</body>






mailcheck.jsp
<body>
<p>Session ID：<%=session.getId() %></p>
<%
String name = null;
String password = null;
name = request.getParameter("username");
password = request.getParameter("password");
if(name != null){
session.setAttribute("username", name);
session.setAttribute("password", password);
}else
name = (String)session.getAttribute("username");
password = (String)session.getAttribute("password");

if(name == null & password == null ){
%>
<jsp:forward page="maillogin.jsp"/>
<%
}
%>


<p>当前用户：<%=name %></p>
<p>您的信箱中有0封邮件未读</p>


<a href="maillogin.jsp">登陆</a>   
<a href="mailout.jsp">退出</a>



</body>