struts中出现HTTP Status 500的错误怎么解决？

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException
org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:535)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:433)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)

root cause

java.lang.NullPointerException
com.action.UserInfoAction.executeUpdate(UserInfoAction.java:43)
com.action.UserInfoAction.execute(UserInfoAction.java:60)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)

note The full stack trace of the root cause is available in the Apache Tomcat/5.5.27 logs
若需要详细的代码可以留下邮箱，有人帮我用Mysql调试的时一点问题都没有,在我电脑上运行就出现该问题,我实在是无法解决,所以请高手指点.要代码的话可以留下邮箱.
try{
四十三：Statement stmt=con.createStatement();
int iCount=stmt.executeUpdate(sql);
System.out.println("操作成功，所影响的记录为"+String.valueOf(iCount));
}
catch(SQLException e){
}
return true;
}
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)throws SQLException{
UserInfoActionForm userInfoActionForm=(UserInfoActionForm)form;
userInfoActionForm.setName(userInfoActionForm.getName());
userInfoActionForm.setAge(userInfoActionForm.getAge());
userInfoActionForm.setSex(userInfoActionForm.getSex());
userInfoActionForm.setProfession(userInfoActionForm.getProfession());

String messager="添加用户失败！！！";
六十三：if(executeUpdate(userInfoActionForm)){
messager="添加用户成功！！！";

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