code: private function groupIssuesByLabels(array $issues, ChangelogConfig $changelogConfig) : array
      {
          $issueGroups = [];
  
          foreach ($this->getIssuesToGroup($issues) as $issue) {
              $groupName = $this->generateIssueGroupName($issue, $changelogConfig);
  
              if (! isset($issueGroups[$groupName])) {
                  $issueGroups[$groupName] = new IssueGroup($groupName);
              }
  
              $issueGroups[$groupName]->addIssue($issue);
          }
  
          return $issueGroups;
      }
docs: @param Issue[] $issues
  
  @return IssueGroup[]