Prior to this PR, `ls` would return `nothing` in an empty directory.
After this PR, it returns an empty `List`. This makes the behaviour of
`ls` more consistent and easier to reason about (IMO).
This was prompted by a user noticing that `ls | where size == 0KB and
type == file` breaks when run in an empty directory:
```
× Input type not supported.
╭─[entry #12:1:1]
1 │ ls | where size == 0KB and type == file
· ─┬ ──┬──
· │ ╰── only list, binary, raw data or range input data is supported
· ╰── input type: nothing
╰────
```
If people agree with this change, let's wait until after the 0.77
release so we have a bit more time to test it.
57ce6a7c66