could not be resolved as a collection/array/map/enumeration/iterator type

由于上传附件form中enctype="multipart/form-data"的没有填写，导致以下后台出现以下错误：

 

tag 'select', field 'list', name 'channelId': The requested list key 'channelList' could not be resolved as a collection/array/map/enumeration/iterator type. Example: people or people.{name} - [unknown location]
    at org.apache.struts2.components.Component.fieldError(Component.java:240)
    at org.apache.struts2.components.Component.findValue(Component.java:361)
    at org.apache.struts2.components.ListUIBean.evaluateExtraParams(ListUIBean.java:80)
    at org.apache.struts2.components.Select.evaluateExtraParams(Select.java:105)
    at org.apache.struts2.components.UIBean.evaluateParams(UIBean.java:864)
    at org.apache.struts2.components.UIBean.end(UIBean.java:516)
    at org.apache.struts2.views.jsp.ComponentTagSupport.doEndTag(ComponentTagSupport.java:42)
    at org.apache.jsp.WEB_002dINF.content.sms.send_002dmessage_002dinput_jsp._jspx_meth_s_005fselect_005f0(send_002dmessage_002dinput_jsp.java:1283)
    at org.apache.jsp.WEB_002dINF.content.sms.send_002dmessage_002dinput_jsp._jspService(send_002dmessage_002dinput_jsp.java:791)