rustc crash with upcall fail "option none"

[erickt]

I'm getting this exception:

rust: upcall fail 'option none', ../src/libcore/option.rs:34
rust: domain main @0x102029600 root task failed

With this reduced (and invalid) code:

use std;
import std::str;

obj a() {
    fn b() {
        c({ |d| });
    }
}