code: func FileChecker(f string) health.Checker {
  	return health.CheckFunc(func() error {
  		absoluteFilePath, err := filepath.Abs(f)
  		if err != nil {
  			return fmt.Errorf("failed to get absolute path for %q: %v", f, err)
  		}
  
  		_, err = os.Stat(absoluteFilePath)
  		if err == nil {
  			return errors.New("file exists")
  		} else if os.IsNotExist(err) {
  			return nil
  		}
  
  		return err
  	})
  }
docs: // FileChecker checks the existence of a file and returns an error
  // if the file exists.