ActivitiesChangesCollection::add

public function add(ActivityChange $activityChange)
{
	$id = $activityChange->getId();
	$existedChange = $this->get($id);
	/** @var $existedChange ActivityChange */
	if ($existedChange)
	{
		$existedChange->applyNewChange($activityChange);
	}
	else
	{
		$this->set($id, $activityChange);
	}
}