I have tried to screen share using the example here: https://demo.flashphoner.com/ from computer that does not have microphone or webcam and here is the error I got:
Please clarify your case: OS version, browser version, has your PC webcam only, microphone only or has no media devices at all.
We reproduced this exception in Chrome 71 on Windows 10 on PC without any media devices (desktop with no mic and webcams connected), but Screen Share example works (see screenshots attached).