private static Runnable removeFileSystemRunnable(URI uri) {
    if (Jimfs.systemProvider == null) {
      // TODO(cgdecker): Use Runnables.doNothing() when it's out of @Beta
      return DO_NOTHING;
    }

    // We have to invoke the SystemJimfsFileSystemProvider.removeFileSystemRunnable(URI)
    // method reflectively since the system-loaded instance of it may be a different class
    // than the one we'd get if we tried to cast it and call it like normal here.
    try {
      Method method =
          Jimfs.systemProvider.getClass().getDeclaredMethod("removeFileSystemRunnable", URI.class);
      return (Runnable) method.invoke(null, uri);
    } catch (NoSuchMethodException | InvocationTargetException | IllegalAccessException e) {
      throw new RuntimeException(
          "Unable to get Runnable for removing the FileSystem from the cache when it is closed", e);
    }
  }
Returns a {@code Runnable} that will remove the file system with the given {@code URI} from the
system provider's cache when called.
jimfs/src/main/java/com/google/common/jimfs/JimfsFileSystems.java