Crash on writing to /dev/null on macOS

[aaronjeline]

Attempting to use Eio.Flow.copy_string when stdout points to /dev/null crashes. main.ml:

open Eio

let main env =
    let stdout = Stdenv.stdout env in
    Eio.Flow.copy_string "Hello world!" stdout;
    ()

let () = Eio_main.run main

dune:

(executable
 (public_name demo)
 (name main)
 (libraries eio_main demo))

Interacting with it:

% dune exec demo
Hello world!
% dune exec demo > out
% cat out -p
Hello world!
% dune exec demo > /dev/null
Fatal error: exception File "lib_eio_posix/sched.ml", line 155, characters 2-8: Assertion failed

Eio version: 1.1