a BigDecimal field in Action Form can't be generated for struts's validation.xml

Hello all,
I'm using Xdoclet to generate action form validation files, and I  found the following problem, In action form , BigDecimal field can't be generated in validation.xml , Have you  encountered  the similar problem?
my actionform is the below:
package web.form;
import java.io.Serializable;
import java.math.BigDecimal;
import org.apache.struts.validator.ValidatorForm;

/**
 * @struts.form 
 *    name ="testForm"  
 *    include-all="true"
 * @author fisher
 *
 */
public class TestForm extends ValidatorForm implements Serializable{
 
 private Long id;
 private String name;
 private BigDecimal capital;
 
 public Long getId() {
  return id;
 }
 public String getName() {
  return name;
 }
 public BigDecimal getCapital() {
  return capital;
 }
 /**
  * @struts.validator 
  *   type = "required"
  * @struts.validator-args 
  *   arg0resource="testForm.id"
  * @param id
  */
 public void setId(Long id) {
  this.id = id;
 }
 /**
  * @struts.validator 
  *   type = "required"
  * @struts.validator-args 
  *   arg0resource="testForm.name"
  * @param name
  */
 public void setName(String name) {
  this.name = name;
 }
 /**
  * @struts.validator 
  *   type = "required"
  * @struts.validator-args 
  *   arg0resource="testForm.capital"
  * @param capital
  */
 public void setCapital(BigDecimal capital) {
  this.capital = capital;
 }
  
}

ant webdoclet  task define as:
 <target name="webdoclet" depends="init">
   <webdoclet
       mergedir="${struts-merge}"
       destdir="${struts}"
       excludedtags="@version,@author"
       force="${xdoclet.force}">
     <fileset dir="${src}">
       <include name="**/*Form.java"/>
       <include name="**/*Action.java"/>
     </fileset>
     <strutsconfigxml 
             version="1.2" validateXML="true"/>
    <strutsvalidationxml
      version="1.1.3" validateXML="true" />
   </webdoclet>
 </target>
  run webdoclet task, i found the testForm in validation.xml as following:
       <form name="testForm">
              <field property="id"
                     depends="required">
                  <arg0
                    key="testForm.id"
                  />
              </field>
              <field property="name"
                     depends="required">
                  <arg0
                    key="testForm.name"
                  />
              </field>
      </form>
   TestForm's property capital isn't in validation.xml, that's why,?
   thanks for your time.
  --------------------------------
   fisher