java - Exception while iterating in JSP -

i have class product has field list<productcategorydetail> , productcategorydetail has field of category type , category has field list<subcategory>.

product   |   |-----        list<productcategorydetail>                  |                  |----category                          |                          |---------list<subcategory> 

my objective iterate on list of productcategorydetail object product.

i using following code in jsp:

<c:foreach items="${product.productcategorydetails}" var="productcategorydetails" varstatus="status">     <tr id="category_row">         <td>             <form:label path="productcategorydetails[${status.index}].category">category</form:label>         </td>         <td>             <form:select cssstyle="width:134px" path="productcategorydetails[${status.index}].category.id" cssclass="category">                 <form:options items="${categories}" itemvalue="id" itemlabel="name"/>             </form:select>         </td>         <td>             <form:label path="productcategorydetails[${status.index}].subcategory">subcategory</form:label>         </td>         <td>             <form:select cssstyle="width:134px" path="productcategorydetails[${status.index}].subcategory.id" cssclass="subcategory">                 <form:options items="productcategorydetails[${status.index}].category.subcategories" itemvalue="id" itemlabel="name"/>             </form:select>         </td>     </tr> 

categories drop down working fine subcategories drop down not getting created , throwing following exception:

16:19:17,342 error http-bio-8080-exec-10 form.optionstag:82 - type [java.lang.string] not valid option items javax.servlet.jsp.jspexception: type [java.lang.string] not valid option items