docs: private @Nullable StatFs updateStatsHelper(@Nullable StatFs statfs, @Nullable File dir) {
      if(dir == null || !dir.exists()) {
        // The path does not exist, do not track stats for it.
        return null;
      }
  
      try {
        if (statfs == null) {
          // Create a new StatFs object for this path.
          statfs = createStatFs(dir.getAbsolutePath());
        } else {
          // Call restat and keep the existing StatFs object.
          statfs.restat(dir.getAbsolutePath());
        }
      } catch (IllegalArgumentException ex) {
        // Invalidate the StatFs object for this directory. The native StatFs implementation throws
        // IllegalArgumentException in the case that the statfs() system call fails and it invalidates
        // its internal data structures so subsequent calls against the StatFs object will fail or
        // throw (so we should make no more calls on the object). The most likely reason for this call
        // to fail is because the provided path no longer exists. The next call to updateStats() will
        // a new statfs object if the path exists. This will handle the case that a path is unmounted
        // and later remounted (but it has to have been mounted when this object was initialized).
        statfs = null;
      } catch (Throwable ex) {
        // Any other exception types are not expected and should be propagated as runtime errors.
        throw Throwables.propagate(ex);
      }
  
      return statfs;
    }