[scenario 4] 2> redirection is not working

This example does not work:

```bash
grep foo /shared/data/bank/homo_sapiens 2> error.log
```

The `error.log` is created but is empty. The error message is printed in the terminal:

```bash
$ grep foo /shared/data/bank/homo_sapiens 2> error.log
(null): /shared/data/bank/homo_sapiens: Is a directory
```