public function isEmailNotTaken( $email, $fields = array() )
    {
        $fields = (object) $fields;

        return $this->getMapper()
                    ->isEmailTaken(
                          $email,
                          empty( $fields->id ) ? null : $fields->id
                      )
               ? 'user.action.register.email.taken'
               : true;
    }