[webrtc-pc] Should empty (not omitted) username or credential throw in the RTCPeerConnection constructor?

foolip has just created a new issue for 
https://github.com/w3c/webrtc-pc:

== Should empty (not omitted) username or credential throw in the 
RTCPeerConnection constructor? ==
This throws in Firefox: `new 
RTCPeerConnection({iceServers:[{urls:'turn:foo.com',username:'',credential:''}]})`

But the spec says "If scheme name is turn or turns, and either of 
server.username or server.credential are omitted, then throw an 
InvalidAccessError and abort these steps."

If the Firefox behavior makes sense, the spec should say "empty or 
omitted" and 
https://github.com/w3c/web-platform-tests/blob/master/webrtc/rtcpeerconnection/rtcpeerconnection-constructor.html
 needs to be updated.

Please view or discuss this issue at 
https://github.com/w3c/webrtc-pc/issues/885 using your GitHub account