Apache Tomcat/4.0.6 - HTTP Status 500 - Internal Server Error错误

test4.jsp:
<%@ page contentType="text/html; charset=gb2312" language="java" %>
<html>
<head>
<title>forward</title>
</head>
<body>
<form action="" method="post" name="form">
  请输入姓名：<input type="text" name="names"><br />
  请输入验证码：<input type="text" name="password"><br />
    <input type="submit" name="submit" value="验证">
<%
String names=request.getParameter("names");
String password=request.getParameter("password");
if(password.equals("good")){
%>
<jsp:forward page="test4_1.jsp">
  <jsp:param name="g" value="<%=names%>"/>
  <jsp:param name="mess" value="you are success!"/>
</jsp:forward>
<%
}else{
%>
<jsp:forward page="test4_1.jsp">
  <jsp:param name="g" value="<%=names%>"/>
  <jsp:param name="mess" value="your password is mistake!"/>
</jsp:forward>
<%
}
%>
</form>
</body>
</html>test4_1.jsp:
<%@ page contentType="text/html; charset=GB18030" %>
<html>
<head>
<title>
forward
</title>
</head>
<body>
hello:<%=(String)request.getParameter("g")%>,
<%=(String)request.getParameter("mess")%>
</body>
</html>
运行test4.jsp页面，有错误。
Apache Tomcat/4.0.6 - HTTP Status 500 - Internal Server Error
ype Exception reportmessage Internal Server Errordescription The server encountered an internal error (Internal Server Error) that prevented it from fulfilling this request.exception java.lang.NullPointerException
 at org.apache.jsp.test4$jsp._jspService(test4$jsp.java:61)
 at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:107)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
 at org.apache.jasper.servlet.JspServlet$JspServletWrapper.service(JspServlet.java:201)
 at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:381)
 at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:473)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:243)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
 at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
 at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:190)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
 at org.apache.catalina.valves.CertificatesValve.invoke(CertificatesValve.java:246)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
 at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
 at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
 at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2347)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
 at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:170)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:170)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
 at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
 at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
 at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
 at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
 at org.apache.catalina.connector.http.HttpProcessor.process(HttpProcessor.java:1027)
 at org.apache.catalina.connector.http.HttpProcessor.run(HttpProcessor.java:1125)
 at java.lang.Thread.run(Thread.java:534)