Unboxed closures: cannot invoke no-argument closures

[netvl]

#![feature(unboxed_closures, unboxed_closure_sugar)]

fn make_adder(a: int, b: int) -> Box<|&:| -> int> {
    (box |&:| a + b) as Box<|&:| -> int>
}

fn main() {
    println!("{}", make_adder(1, 2).call(()));
}

This code does not compile with this error:

<anon>:8:42: 8:44 error: mismatched types: expected `()` but found `()` (expected tuple but found ())
<anon>:8     println!("{}", make_adder(1, 2).call(()));
                                                  ^~
note: in expansion of format_args!
<std macros>:2:23: 2:77 note: expansion site
<std macros>:1:1: 3:2 note: in expansion of println!
<anon>:8:5: 8:47 note: expansion site
error: aborting due to previous error

Naturally, call() without arguments does not work, but I know of no other way to pass zero argument to the closure.

[japaric]

This code is working on master, it must've been fixed by one of many unboxed closure PRs that have landed in the past 24 hours.

[japaric]

Found it, duplicate of #16168, fixed by PR #16637.

[alexcrichton]

Thanks for investigating @japaric!