code: public function getFileContent($file, $identifier)
      {
          $command = sprintf('fossil cat -r %s %s', ProcessExecutor::escape($identifier), ProcessExecutor::escape($file));
          $this->process->execute($command, $content, $this->checkoutDir);
  
          if (!trim($content)) {
              return null;
          }
  
          return $content;
      }
docs: {@inheritdoc}