public function isDisplayNameAvailable( $displayName, $fields = array() )
    {
        $fields      = (object) $fields;
        $displayName = Structure::trimDisplayName( $displayName );

        if ( 3 > mb_strlen( $displayName ) )
        {
            return 'user.action.register.displayName.tooShort';
        }

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