code: @Override
      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);
      }
docs: Provides a message from a resource bundle <code>activejdbc_messages</code>.
  If an there was no validation error generated for the requested attribute, returns null.
  
  @param attributeName name of attribute in error.
  @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.