scala/async — pull request #75 by retronym (2014-06-14 10:51:37+00:00)
Title: Avoid NotImplementedError awaiting a Future[Nothing]

`gen.mkZero(NothingTpe)` gives the tree `Predef.???`. Instead, we should leave
the `await` field uninitialized with `ValDef(..., rhs = EmptyTree)`.

Fixes #66