If an `LF` or double quote must be encoded into `<path>` shell-style
quoting should be used, e.g. `"path/with\n and \" in it"`.
+Additionally, in `040000` mode, `<path>` may also be an empty string
+(`""`) to specify the root of the tree.
+
The value of `<path>` must be in canonical form. That is it must not:
* contain an empty directory component (e.g. `foo//bar` is invalid),