code: public function getRootIdentifier()
      {
          if (null === $this->rootIdentifier) {
              $this->rootIdentifier = 'master';
  
              // select currently checked out branch if master is not available
              $this->process->execute('git branch --no-color', $output, $this->repoDir);
              $branches = $this->process->splitLines($output);
              if (!in_array('* master', $branches)) {
                  foreach ($branches as $branch) {
                      if ($branch && preg_match('{^\* +(\S+)}', $branch, $match)) {
                          $this->rootIdentifier = $match[1];
                          break;
                      }
                  }
              }
          }
  
          return $this->rootIdentifier;
      }
docs: {@inheritDoc}