急救 关于SmartUpload上传图片的问题

我用了一个SmartUpload组件上传图片   抛出了如下异常信息   各位大哥帮小弟解决下啊 
javax.servlet.ServletException:   java.lang.NullPointerException 
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:710) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:803) root   cause java.lang.NullPointerException 
com.jspsmart.upload.SmartUpload.initialize(SmartUpload.java:153) 
com.ditian.sjjy.struts.action.PresumeAction.execute(PresumeAction.java:95) 
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:710) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:803) 
/****************************************************************/ 
jsp页面如下   
<form   name= "resume "   method= "post "   action= "presume.do "   onsubmit= "return   formcheck(); "   >   
上传个人照片: <input   type= "file "   name= "photo "   id= "photo "/> <br> 
              验证码: <input   type= "text "   name= "check "   id= "check "/>   <img   id= "randImage "   src= "jspPage/image.jsp "   /> 
              <a   href= "javascript:loadimage(); "> 看不清点我 </a> 
              <br> 
              <input   type= "submit "   value= "保存 "   name= "ok "   >   
        </form>   /*******************************************************/ 
    PresumeAction   上传代码如下   
public   ActionForward   execute(ActionMapping   mapping,   ActionForm   form, 
HttpServletRequest   request,   HttpServletResponse   response)   throws   UnsupportedEncodingException     { 
PresumeForm   presumeForm   =   (PresumeForm)   form;//   TODO   Auto-generated   method   stub 
        SmartUpload   sUpload=new   SmartUpload(); 
String   filedir= "upload/ "; 
long   maxsize=50*1024;//50kb 
try   { 
sUpload.initialize((PageContext)   PageContext); 
sUpload.setMaxFileSize(maxsize); 
}   catch   (ServletException   e)   { 
//   TODO   Auto-generated   catch   block 
e.printStackTrace(); 
} 
try   { 
sUpload.upload(); 
sUpload.save(filedir,SmartUpload.SAVE_VIRTUAL); }   catch   (ServletException   e)   { 
//   TODO   Auto-generated   catch   block 
e.printStackTrace(); 
}   catch   (IOException   e)   { 
//   TODO   Auto-generated   catch   block 
e.printStackTrace(); 
}   catch   (SmartUploadException   e)   { 
//   TODO   Auto-generated   catch   block 
e.printStackTrace(); 
} 
return   null; 
｝