FsPermission string constructor does not recognize sticky bit

FsPermissions's string constructor breaks on valid permission strings, like "1777".

This is because FsPermission class naïvely uses UmaskParser to do it’s parsing of permissions: (from source code):
public FsPermission(String mode) {
this((new UmaskParser(mode)).getUMask());
}

The mode string UMask accepts is subtly different (esp wrt sticky bit), so parsing Umask is not the same as parsing FsPermission.