Validation framework not working for multiple selections!!

I am using struts and the ValidatorPlugIn. I am having some issues trying to validate input for an options box. I have the validation working correctly if within the struts-config.xml file the form-property type="java.lang.String" (I can validate the form-property value in the example listed below).

My issue is that I can't validate when the form-property is of type="java.lang.String[]" (I can't validate the form-property assets in the example listed below). Do I need to include something in the validation.xml that indicates I am working with type="java.lang.String[]"

ca_search.jsp (snippets):

<html:form action="/caSearch" target="main" onsubmit="return validateCaSearchForm(this);">

<html:select size="3" property="assets" style="news" multiple="true">
<html ptions collection="assetTypes" property="property" labelProperty="labelProperty"/>
</html:select>

<html:javascript formName="caSearchForm"/>

struts-config.xml:

<form-bean name="caSearchForm" type="org.apache.struts.validator.DynaValidatorForm">
<form-property name="assets" type="java.lang.String[]" />
<form-property name="value" type="java.lang.String" />
<form-property name="sites" type="java.lang.String" />
<form-property name="searchFor" type="java.lang.String" />
<form-property name="sortBy" type="java.lang.String" />
<form-property name="departments" type="java.lang.String" />
<form-property name="action" type="java.lang.String" />
</form-bean>

validation.xml:

<form name="caSearchForm">
<field property="value" depends="required">
<arg0 key="ca_search.val"/>
</field>
<field property="assets" depends="required">
<arg0 key="ca_search.assets"/>
</field>
</form>

Again, I have the validation working correctly when form-property is of type="java.lang.String". I can't however validate when the form-property is of type="java.lang.String[]".