JPS中List中的数据我已经封装在一个控制层了，但还是不行

Servlet.service() for servlet jsp threw exception
tag 'select', field 'list', name 'docTypeInfo.docTypeCode': The requested list key 'docTypeList' could not be resolved as a collection/array/map/enumeration/iterator type. Example: people or people.{name} - [unknown location]
代码如下：<body>
<div class="dialogBorder">
<s:form id="myform" action="addDocTypeCutTmpMapping" target="_self" namespace="/app"
theme="simple" validate="true">
<table class="lsTable" border="0">
<tr>
<td class="titleFont" nowrap="nowrap">
新增切片模板信息
</td>

</tr>
<tr>
<td align="center">
<div class="crossBar"></div>
</td>
</tr>
<tr>
<td valign="top" height="30%" align="center">
<table border="0" class="innerTable" cellpadding="2">
<tr>
<td class="itemFont" nowrap="nowrap">
文档类型编号:
</td>
<td>
<s:select listKey="id"  listValue="name"  list="docTypeList" name="docTypeInfo.docTypeCode"  headerKey="0" headerValue="--请选择--">
    </s:select>