code: func (c *Cache) getOrRemove(id string) hugio.ReadSeekCloser {
  	if c.maxAge == 0 {
  		// No caching.
  		return nil
  	}
  
  	if c.maxAge > 0 {
  		fi, err := c.Fs.Stat(id)
  		if err != nil {
  			return nil
  		}
  
  		if c.isExpired(fi.ModTime()) {
  			c.Fs.Remove(id)
  			return nil
  		}
  	}
  
  	f, err := c.Fs.Open(id)
  
  	if err != nil {
  		return nil
  	}
  
  	return f
  }
docs: // getOrRemove gets the file with the given id. If it's expired, it will
  // be removed.