求助

servlet: public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
                  this.doPost(request, response);
 
}  
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
 
 String action=request.getParameter("action");
 if(action==null)
 {
action=""; 
 }
 if(action.equals("add"))
 {
this.addmotherboard(request, response);
 }
 
}
 public void addmotherboard(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException 
 {
 motherboard mboarddao=new motherboard();
 motherboardjb  mboardjavabean=new motherboardjb();
 RequestDispatcher rd=null;
 mboardjavabean.setMotherBoard_Name(request.getParameter("motherboardname"));
 mboardjavabean.setInt_MotherBoard_Place(trans.strToint(request.getParameter("motherboardplace")));
 boolean fm=mboarddao.operateMotherBoard("add", mboardjavabean);
 if(!fm)
 {
 rd=request.getRequestDispatcher("addmotherboard.jsp");
 rd.forward(request, response);
 
 }
 else 
 {
  System.out.print("javascript:alert('添加成功')");
  response.sendRedirect("addmotherboard.jsp");
 
 }
  dao:if(operation.equals("add"))
{
 sql="insert into MotherBoard values('"+single.getMotherBoard_Name()+"','"+single.getInt_MotherBoard_Place()+"')"; 
}
  报错：2011-11-6 23:27:12 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet MboardServlet threw exception
java.lang.NullPointerException
at com.dao.motherboard.operateMotherBoard(motherboard.java:36)
at com.servlet.MboardServlet.addmotherboard(MboardServlet.java:64)
at com.servlet.MboardServlet.doPost(MboardServlet.java:53)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:228)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
at java.lang.Thread.run(Thread.java:619)