C++ lambda used in std::thread crash

Question

This my code:

std::thread t([](){
  int ret = func();
  if (ret != 0){
    return false;
  }
});
t.detach();

As this code, compiler deduce the lambda return value type is bool, so when ret==0, the lambda has not a return value, then program is crash. Add return true can solve this problem, I want to now why?

I want to know, lambda return behavior when used in thread.