Theme Options - Not working :(

function theme_options_validate( $input ) {
    if ($input['slidercats'] != '') {
        $slidercats = $input['slidercats'];
        $slidercats_array = explode( ',', $slidercats );
        $slidercats_array = array_unique( $slidercats_array );
        $slidercats_array = array_map('intval', $slidercats_array );

        foreach($slidercats_array AS $i => $value)
        {
            $cat = get_category($i); // cat_ID
            if ( empty( $cat ) )
                unset($slidercats_array[$i]);
        }

        $input['slidercats'] = implode(",", $slidercats_array);

    }

    return $input;
}