JSP中 ！The server encountered an internal error () that prevented it from fulfill

为什么我运行
<%@ page language="java" contentType="text/html" pageEncoding="gb2312"%>
<html>
    <head>
        <title>request中的getparameter()方法</title>
    </head>
    <body>
        <%--在这里设定request得到参数的字符编码，否则中文会出现乱码 --%>
        <%request.setCharacterEncoding("gb2312");%>
        得到用户输入的信息：<p>
            <font color=red>姓名：<%=request.getParameter("name").toString()%><p>
                    性别：<%=request.getParameter("sex").toString()%><p>
                    年龄：<%=request.getParameter("age").toString()%><p>
            </font>
            获取按钮标记名：
            <font color=blue>
                <%=request.getParameter("submit").toString()%>
            </font>
    </body>
</html>
时候会显示如下错误
type Exception reportmessagedescriptionThe server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException: java.lang.NullPointerException
root cause 
谁能帮我解答 谢谢