Type [java.lang.String] is not valid for option items upon migrating from Spring 3.0.6 to 3.2.3 - spring

Question

I am working on migrating a dynamic web project from Spring 3.0.6 to 3.2.3. Prior to this migration, we had no issue with our dropdowns. However, after migrating, we get the following error:
Exception created : com.ibm.websphere.servlet.error.ServletErrorReport: javax.servlet.jsp.JspException: Type [java.lang.String] is not valid for option items
I've removed all the code to isolate the issue, so below is the relevant code. Please let me know if any further information is needed. The thing that puzzles me is that the List isn't even String based. I realize that the JSP will treat the values as String for the options, but my understanding is that there is a built-in PropertyEditor that would do this translation.
Controller:
#RequestMapping("/reports-menu.html")
public String showReportsHome(#ModelAttribute("reportForm")ReportForm reportForm, Model model, HttpSession session, HttpServletResponse response, HttpServletRequest request) {
List<Integer> intList = new ArrayList<Integer>();
intList.add(1);
intList.add(2);
intList.add(3);
model.addAttribute("intList", intList);
return "reports-home-int";
}
JSP:
<%# taglib uri="/WEB-INF/tld/c.tld" prefix="c" %>
<%# taglib uri="/WEB-INF/tld/fmt.tld" prefix="fmt" %>
<%# taglib uri="http://www.springframework.org/tags/form" prefix="form"%>
<%# taglib uri="http://www.springframework.org/tags" prefix="spring" %>
<%# taglib uri="/WEB-INF/tld/sbp.tld" prefix="sbp" %>
<form:form name="report_form" method="POST" modelAttribute="reportForm" action="reports-menu.html" id="report_form">
<form:hidden path="download" id="form_download"/>
<form:hidden path="sortDirection" />
<form:hidden path="sortBy"/>
<input type="hidden" name="reset"/>
<div align="left">
<table border="0">
<tr>
<td><b>Mailer Name</b></td>
<td>
<form:select path="mailerCond">
<form:options items="${intList}" />
</form:select>
</td>
</tr>
</table>
</div>
</form:form>