ISBN stereotype and validation class

Hi Javi 
I have used ISBN stereotype and validation class in qaManager and want to share same with OpenXava. 

Following was done 
1) Added to default-size.xml 
<for-stereotype name="ISBN" size="13"/> 

2) Added to editors.xml 
<editor url="textEditor.jsp"> 
<for-stereotype stereotype="ISBN"/> 
</editor> 

3) Added to Stereotype-type-default.xml 
<for stereotype="ISBN" type="String"/> 

4) Added to messages_en.properties file 

isbn_validation_error={0} must be a valid ISBN address 

5) Validation class 

package org.openxava.validators;

import org.openxava.validators.IPropertyValidator;
import org.openxava.util.Messages;
/**
*
* @author Janesh Kodikara
*/

public class ISBNValidator implements IPropertyValidator {

    private  org.apache.commons.validator.ISBNValidator validator = new org.apache.commons.validator.ISBNValidator();

    public void validate(Messages errors, Object value, String propertyName, String modelName) throws Exception {

        if (value == null || value.toString().length() ==0 ) return;

        if (! validator.isValid(value.toString())) {
           errors.add("isbn_validation_error", propertyName);
        }
    }

}

Appreciate your comments to improve the same. 

Thanking You
Janesh