{namespace nr=Stratis\StratisNewsReservation\ViewHelpers}
{nr:availablePlaces(newsId: newsItem.uid) -> v:variable.set(name: 'availablePlaces')}

<f:if condition="{availablePlaces} > 0">
    <f:link.page pageUid="{stratisPages.reservationPage}" additionalParams="{news_id:newsItem.uid}" class="btn heading__btn">{s:l(key:'reserver')}</f:link.page>
</f:if>