private function validateMemberBranch() {
    /** @var \Drupal\node\Entity\Node $campaign Campaign node object. */
    $campaign = $this->getCampaign();
    /** @var \Drupal\openy_campaign\Entity\Member $member Temporary Member object. Will be saved by submit. */
    $member = $this->getMember();

    $branchesField = $campaign->get('field_campaign_branch_target')->getValue();
    $campaignBranches = [];
    foreach ($branchesField as $branch) {
      $campaignBranches[] = $branch['target_id'];
    }

    $memberBranch = $member->getBranchId();

    if (in_array($memberBranch, $campaignBranches)) {
      return ['status' => TRUE, 'error' => ''];
    }

    return ['status' => FALSE, 'error' => t('Branch is not included.')->render()];
  }