页面运行出错：弹出 sub_ill.0.0为空或不是对象，求解！

<%@ page language="java" pageEncoding="gb2312"%>
<%@ taglib uri="http://jakarta.apache.org/struts/tags-bean"
prefix="bean"%>
<%@ taglib uri="http://jakarta.apache.org/struts/tags-html"
prefix="html"%>
 
<html>

<title>JSP for AdvisoryInputForm form</title>
<style type="text/css">
<!--
.STYLE3 {font-size: 16px; font-weight: bold; }
.STYLE4 {font-size: 14px}
.STYLE5 {font-size: 14}
-->
        </style>

<script type="text/javascript" src="../../dwr/interface/illDeal.js"></script>
<script type='text/javascript' src='../../dwr/engine.js'></script>
<script type='text/javascript' src='../../dwr/util.js'></script>

<body bgcolor="f0f0f0" onLoad="loadData()">
<html:form action="/admin/advisory/advisoryInput?id=${caseId}">
<table width="600" border="0" align="center">
<tr>
<td width="68" height="31">&nbsp; </td>
<td width="245">&nbsp; </td>
<td width="241">&nbsp; </td>
<td width="28">&nbsp; </td>
</tr>
<tr>
<td>&nbsp; </td>
<td align="left">
<span class="STYLE3">姓名：${name }</span> </td>
<td align="left">
<span class="STYLE3">学号：${stuId }</span> </td>
<td>&nbsp; </td>
</tr>
<tr>
<td>&nbsp; </td>
<td align="left">&nbsp; </td>
<td align="left">&nbsp; </td>
<td>&nbsp; </td>
</tr>
<tr>
<td height="100">&nbsp; </td>
<td colspan="2" align="left" valign="top">
<span class="STYLE4">问题简述：<br> 
  <html:textarea
property="main_problem" rows="5" cols="60" /> <html:errors
property="main_problem" /> </span> </td>
<td>&nbsp; </td>
</tr>
<tr>
<td height="100">&nbsp; </td>
<td colspan="2" align="left" valign="top">
<span class="STYLE4">主诉：<br> 
  <html:textarea
property="mainTell" rows="5" cols="60" /> <html:errors
property="mainTell" /> </span> </td>
<td>&nbsp; </td>
</tr>
<tr>
<td height="100">&nbsp; </td>
<td colspan="2" align="left" valign="top">
<span class="STYLE4">咨询过程：<br> 
  <html:textarea
property="consultation_process" rows="5" cols="60" /> <html:errors
property="consultation_process" /> </span> </td>
<td>&nbsp; </td>
</tr>
<tr>
<td height="100">&nbsp; </td>
<td colspan="2" align="left" valign="top">
<span class="STYLE4">评估： <br> <html:textarea
property="evaluate" rows="5" cols="60" /> <html:errors
property="evaluate" /> </span> </td>
<td>&nbsp; </td>
</tr>
<tr>
<td height="100">&nbsp; </td>
<td colspan="2" align="left" valign="top">
<span class="STYLE4">建议：<br> 
  <html:textarea
property="suggest" rows="5" cols="60" /> <html:errors
property="suggest" /> </span> </td>
<td>&nbsp; </td>
</tr>
<tr>
<td>&nbsp; </td>
<td align="left" valign="top">
<span class="STYLE5">咨询师： 
<html:text property="teacher" value="${teacherName}" />
  <html:errors property="teacher" /> </span> </td>
<td align="left" valign="top">
<span class="STYLE5">时间：
  <html:text property="today" value="${today}"></html:text></span> </td>
<td>&nbsp; </td>
</tr>
<tr>
<td>&nbsp; </td>
<td colspan="2" align="left" valign="top">
<span class="STYLE5">病情分类：</span><span class="STYLE5">
<html:select
property="main_ill_type" onchange="main_ill_change(this)">

</html:select> 
<html:select property="ill_type" onchange="sub_ill_change(this)"></html:select>
<html:errors property="ill_type" /> </span><span>
<html:select property="subsubill_type">

</html:select> 
<html:errors property="subsubill_type" /> </span>   <span class="STYLE5"></span> </td>
<td>&nbsp; </td>
</tr>
<tr>
<td>&nbsp; </td>
<td colspan="2" align="left">
<span class="STYLE5">是否连续咨询： 
<html:select property="next">

  <html:option value="no" >否</html:option><html:option value="yes">是</html:option></html:select></span> </td>
<td>&nbsp; </td>
</tr>
<tr>
<td>&nbsp; </td>
<td align="right">
<html:submit>提交</html:submit>
&nbsp; </td>
<td align="left">
<html:cancel>取消</html:cancel>
&nbsp; </td>
<td>&nbsp; </td>
</tr>
<tr>
<td>&nbsp; </td>
<td>&nbsp; </td>
<td>&nbsp; </td>
<td>&nbsp; </td>
</tr>
  </table>
</html:form>
</body>
<script language="javascript" type="text/javascript">

var main_ill=new Array();//主目录数据结构
var sub_ill=new Array();//子目录数据结构
var subsub_ill=new Array();

var main_select=document.getElementsByName("main_ill_type")[0];//主目录显示框
var sub_select=document.getElementsByName("ill_type")[0];//子目录显示框
var subsub_select=document.getElementsByName("subsubill_type")[0];
function loadData(){
illDeal.getMainAll(function(list){
main_ill=list;
update_main();
});
illDeal.getSubAll(function(list){
sub_ill=list;
update_sub(main_ill[0][1]);
});
illDeal.getSubsubAll(function(list){
subsub_ill=list;
update_subsub(sub_ill[0][0][1]);
});
}

//主目录改变

function main_ill_change(item){
var main_id=item.value;
update_sub(main_id);
}
//子目录改变

function sub_ill_change(item){
var sub_id=item.value;
update_subsub(sub_id);
}

//刷新主目录数据

function update_main(){
main_select.options.length=0;
for(var i=0;i<main_ill.length;i++){
main_select.options.add(new Option(main_ill[i][0],main_ill[i][1]));
}
}
//刷新子目录

function update_sub(main_id){
sub_select.options.length=0;
for(var i=0;i<sub_ill.length;i++){
var sub_list=sub_ill[i];
if(sub_list[0][2]==main_id){
for(var j=0;j<sub_list.length;j++){
sub_select.options.add(new Option(sub_list[j][0],sub_list[j][1]));
}
}
}
}

//刷新子子目录

function update_subsub(sub_id){
subsub_select.options.length=0;
for(var i=0;i<subsub_ill.length;i++){
var subsub_list=subsub_ill[i];
if(subsub_list[0][2]==sub_id){
for(var j=0;j<subsub_list.length;j++){
subsub_select.options.add(new Option(subsub_list[j][0],subsub_list[j][1]));
}
}
}
}
</script> 
</html>