JQuery EsayUI ComboBox 在chrome 报 An invalid form control with name='' is not focusable.

<form method="post" name="userForm" url="**">
<input class="easyui-combobox" name="rId" required="true" data-options="valueField:'id',textField:'text',url:'url'" />
<input type="submit" class="buttons" value="保存"/>
</form>

<form method="post" name="userForm" url="**">
<input class="easyui-combobox" name="rId" required="true" data-options="valueField:'id',textField:'text',url:'url'" />
<input type="button" class="buttons" value="保存" onclick="add()"/>
</form>
<script type="text/javascript">
function add(){
if ($('#userForm').form('validate')){
$('#userForm').submit();
}
}
</script>