PipeListener.Close error

In worker/uniter/uniter.go, we had a cleanup function that called u.tomb.Kill(runListener.Close()). On windows, this is an npipe, where Close() is returning an "Element not found".

Why does this error return from npipe/PipeListener.Close()? Is it a problem with how we're using it, or is this something that can/should be ignored?

[Edited]
