Hi all.
This is my first contribution to Rust and fixes an issue causing an invalid error message to be presented to the user when using unit struct as length of a repeat expression, issue #27008. The solution is based on suggestions by @oli-obk, but as I'm a complete newbie to this, I have no clue if I got them right :)
The biggest concern I have is that if the `NodeId` I'm returning is the correct one or not (it's not meaningful in this case but I think it would be nice to get it right).