点击提交后出现java.lang.NumberFormatException: null异常，求大神回帖~

异常：
java.lang.NumberFormatException: null
java.lang.Integer.parseInt(Unknown Source)
java.lang.Integer.parseInt(Unknown Source)
com.action.OrderDetailServlet.service(OrderDetailServlet.java:39)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
com.util.EncodingFilter.doFilter(EncodingFilter.java:30)
com.util.EncodingFilter.doFilter(EncodingFilter.java:30)
OrderDetailServlet.java的代码：

public class OrderDetailServlet extends HttpServlet {

	public void service(HttpServletRequest request, HttpServletResponse response)

			throws ServletException, IOException {



		response.setContentType("text/html");

		PrintWriter out = response.getWriter();

		

		String orderId = request.getParameter("orderId");

		String meauId = request.getParameter("meauId");

		String num = request.getParameter("num");

		String remark = request.getParameter("remark");

		

		OrderDao dao = new OrderDaoImpl();

		

		OrderDetail od = new OrderDetail();

		

		od.setMenuId(Integer.parseInt(meauId));

		od.setOrderId(Integer.parseInt(orderId));

		od.setNum(Integer.parseInt(num));

		od.setRemark(remark);

		

		dao.saveOrderDetail(od);

		

		out.print(remark);

		

		out.flush();

		out.close();

	}

}

页面orderdish.jsp代码：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%@ page isELIgnored="false" %> 

<%@page import="com.action.*"%>

<%

String path = request.getContextPath();

%>



<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

	<head>

		<meta http-equiv="pragma" content="no-cache" />

		<meta http-equiv="cache-control" content="no-cache" />

		<meta http-equiv="expires" content="0" />

		<meta http-equiv="keywords" content="keyword1,keyword2,keyword3" />

		<meta http-equiv="description" content="This is my page" />

        

        <title>菜品选择</title>

        <style type="text/css">

          body{

             background-image:url(<%=path %>/img/banner.png);

             display:block;

              }

        .tablebox{background-image:url(<%=path %>/img/bg_tm.png);font-size:15px;color:#304031}

        .Add{text-align:right;margin-top:15px;margin-right:45px;}

        .title{font-size:18px}

        div{font-weight:bold}

        

     

   </style>

        

        <script type='text/javascript' src='<%=path %>/dwr/interface/loginService.js'></script>

		<script type='text/javascript' src='<%=path %>/dwr/engine.js'></script>

		<script type='text/javascript' src='<%=path %>/dwr/util.js'></script>

        <script language="javascript">

           var i=0;

           function caipuAll()

           {

               if(i==0)

               {

                   document.getElementById("indicator").style.display="block";

                   loginService.caipuAll(callback);

                   i=1;

               }

               

           }

           function callback(data)

           {

               document.getElementById("indicator").style.display="none";

               DWRUtil.addOptions("meauId",data,"id","name");

           }

           

           function check()

           {

               if(document.formAdd.meauId.value==0)

               { 

                   alert("请选择类别");

                   return false;

               }

               return true;

           }

        </script>

	</head>



	<body>

      <jsp:include page="/admin/daohang.jsp" flush="true"/>

      

        <div class="tablebox">

			<form action="<%=path %>/diancai" name="formAdd" method="post">

      

				     <table width="60%" align="center" border="0" cellpadding="0" cellspacing="0" style="margin:0 auto">

						<tr height="40px">

					        <td colspan="7" align="center" class="title" ><span>   菜品选择</span></td>

					    </tr>

						<tr align='center' height="30">

          

               

            						    <td width="10%" align="right">

						         菜谱列表：

						    </td>

						    <td width="15%" align="left">

						        <table border="0">

							           <tr> 

							               <td>  

							                    

                                             <select name="meauId" id="meauId" onclick="caipuAll()">

									              <option value="0">请选择菜品</option>

									          </select>

							               </td>

							               <td>

							                  <img id="indicator" src="<%=path %>/img/loading.gif" style="display:none"/>

							               </td>

							           </tr>

							    </table>

						    </td>

                <td width="8%"align="right">

                              数量：

                </td>

                <td width="15%"  align="left">

                  

                    <input type="text" name="num" size="20"/>

                </td>

                <td width="7%" align="right">

                     备注：

                </td>

                <td width="10%" align="left">

                  

                    <input type="text" name="remark" size="20"/>

                </td>

                <td width="10%" align="left">

                     

                   <input type="submit" value="提交" onclick="return check()"/>        

						</tr>

					 </table>

			</form>

      </div>

   </body>

</html>