[TYPO3-ttnews] extraItemMarkerProcessor Marker Not substitute !

[Nirmalya]

Hi,
I want to hook in tt_news.
but the error is  Marker Not substituted .
my code is as below
class tx_ttnewssearch {
function extraItemMarkerProcessor($markerArray, $row, $lConf, &$pObj) {
//debug ($markerArray);
   $markerArray['###NEWS_CATEGORY_SELECTION###'] = 'someValue';
return $markerArray;
}

is it necessary to instantiate like:
$local_cObj = t3lib_div::makeInstance('tslib_cObj');
.........any help!
Thank you,
nirmalya,