Not possible to omit a {block} in a snippet import if it's declared in the snippet

If I have this snippet:

```
(foo) {
  reverse_proxy localhost:3000
  {block}
}
```

This works:

```
example.com {
  import foo {
    file_server
  }
}
```

But this doesn't:

```
example.com {
  import foo
}
```

So basically the block is always mandatory and it's not possible to not declare it.

(The example doesn't make any sense, it's basically to show the issue.)