/**
* sets Entity's Main-Fax.
*
* @param Contact|AccountInterface $entity
*/
public function setMainFax($entity)
{
// set main to first entry or to null
if ($entity->getFaxes()->isEmpty()) {
$entity->setMainFax(null);
} else {
$entity->setMainFax($entity->getFaxes()->first()->getFax());
}
}