public static function createMemberCampaign($member, $campaign, $registrationType = 'site') {
    /** @var \Drupal\openy_campaign\Entity\MemberCampaign $memberCampaign Create temporary MemberCampaign object. Will be saved later. */
    $memberCampaign = \Drupal::entityTypeManager()
      ->getStorage('openy_campaign_member_campaign')
      ->create([
        'campaign' => $campaign,
        'member' => $member,
        'registration_type' => $registrationType,
      ]);

    if (($memberCampaign instanceof MemberCampaign === FALSE) || empty($memberCampaign)) {
      \Drupal::logger('openy_campaign')
        ->error('Error while creating MemberCampaign temporary object.');

      return FALSE;
    }

    return $memberCampaign;
  }