我用jbuilder写的一个登陆login.jsp 怎么老是出现错误？
错误提示：
exception   org.apache.jasper.JasperException
  org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:370)
  org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:291)
  org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
  javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root   cause   java.lang.NullPointerException
  grad.util.user.op_user.isLogin(op_user.java:184)
  org.apache.jsp.login_jsp._jspService(org.apache.jsp.login_jsp:59)
  org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
  javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
  org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:322)
  org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:291)
  org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
  javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

------解决方案--------------------
到work目录去看看op_user.java:184行空指针了
------解决方案--------------------
root cause java.lang.NullPointerException
空指针，检查传送的数据
------解决方案--------------------
空指针异常,应该是你页面的数据没有返回