* @return a message from a resource bundle <code>activejdbc_messages</code> as configured in a corresponding
* validator. If an there was no validation error generated for the requested attribute, returns null.
*/
public String get(Object attributeName) {
if(attributeName == null) throw new NullPointerException("attributeName cannot be null");
Validator v = validators.get(attributeName);
return v == null? null:v.formatMessage(locale);
}