calling set() to cppcoro::async_manual_reset_event in coroutine, throw broken promise

[bbqz007]

cppcoro::async_mutex mtx;
                cppcoro::async_manual_reset_event event;
                auto tsk = [&]()->cppcoro::task<>{

                    auto tsk_lock = [&]()->cppcoro::task<>{
                        cppcoro::async_mutex_lock lck = co_await mtx.scoped_lock_async();
                        co_await event;           
                         };
/// terminate called after throwing an instance of 'cppcoro::broken_promise'what():  broken promise
                    auto tsk_unlock = [&]()->cppcoro::task<>{
                        event.set();
                    };
                    co_await cppcoro::when_all(tsk_lock(), tsk_unlock());

[bbqz007]

the problem is that
there is no co_return in a the coro code.
the compiler did not make error even though i did not write the co_return.
in most cases, if my coro code ends with co_await, the code even run ok.
that make me have a wrong idea that there is not need a co_return; if task。

[bbqz007]

yes, all the coro task need the co_return;。

                    auto tsk_lock = [&]()->cppcoro::task<>{
                        co_return;      /// co_return is needed, if not, it return some thing unexpected.
                    };
                    auto tsk_unlock = [&]()->cppcoro::task<>{
                        event.set();
                        co_return;
                    };
                    auto tsk_ev = [&](int i)->cppcoro::task<>{
                        co_await A(i);
                        co_await event;
                        co_await Aa(i);
                        co_await D(i);
                       // co_return;           /// without this, it crash the set() and resume() too.
                    };
                    co_await cppcoro::when_all(tsk_lock(), tsk_ev(1), tsk_ev(2), tsk_ev(3), tsk_unlock());
                };