On my system, sed requires an extension to be provided for the -i option:

```
     -i extension
             Edit files in-place, saving backups with the specified extension.
             If a zero-length extension is given, no backup will be saved.  It
             is not recommended to give a zero-length extension when in-place
             editing files, as you risk corruption or partial content in situ-
             ations where disk space is exhausted, etc.
```