diff --git a/lib/utils.js b/lib/utils.js
index 517f75c..c5f1a2d 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -1,140 +1,140 @@
 'use strict';
 
 import transform from 'sdp-transform';
 import attachMediaStream from 'attachmediastream';
 
 
 class Identity {
-    constructor(uri, displayName='') {
+    constructor(uri, displayName=null) {
         this._uri = uri;
         this._displayName = displayName;
     }
 
     get uri() {
         return this._uri;
     }
 
     get displayName() {
         return this._displayName;
     }
 
     toString() {
         if (!this._displayName) {
             return this._uri;
         } else {
             return `${this._displayName} <${this._uri}>`;
         }
     }
 }
 
 
 function createLocalSdp(pc, type, options) {
     if (type !== 'offer' && type !== 'answer') {
         return Promise.reject('type must be "offer" or "answer", but "' +type+ '" was given');
     }
     let p = new Promise(function(resolve, reject) {
         let createFunc;
         if (type === 'offer' ) {
             createFunc = pc.createOffer;
         } else {
             createFunc = pc.createAnswer;
         }
         createFunc.call(
             pc,
             // success
             function(desc) {
                 pc.setLocalDescription(
                     desc,
                     // success
                     function() {
                         resolve(mungeSdp(pc.localDescription.sdp));
                     },
                     // failure
                     function(error) {
                         reject('Error setting local description: ' + error);
                     }
                 );
             },
             // failure
             function(error) {
                 reject('Error creating local SDP: ' + error);
             },
             options
         );
     });
     return p;
 }
 
 
 function mungeSdp(sdp) {
     let parsedSdp = transform.parse(sdp);
     let h264payload = null;
     let hasProfileLevelId = false;
 
     // try to fix H264 support
     for (let media of parsedSdp.media) {
         if (media.type === 'video') {
             for (let rtp of media.rtp) {
                 if (rtp.codec === 'H264') {
                     h264payload = rtp.payload;
                     break;
                 }
             }
             if (h264payload !== null) {
                 for (let fmtp of media.fmtp) {
                     if (fmtp.payload === h264payload && fmtp.config.indexOf('profile-level-id') !== -1) {
                         hasProfileLevelId = true;
                         break;
                     }
                 }
                 if (!hasProfileLevelId) {
                     media.fmtp.push({payload: h264payload, config: 'profile-level-id=42e01f;packetization-mode=1;level-asymmetry-allowed=1'});
                 }
                 break;
             }
         }
     }
 
     // remove bogus rtcp-fb elements
     for (let media of parsedSdp.media) {
         let payloads = String(media.payloads).split(' ');
         if (media.rtcpFb) {
             media.rtcpFb = media.rtcpFb.filter((item) => {
                 return payloads.indexOf(String(item.payload)) !== -1;
             });
         }
     }
 
     return transform.write(parsedSdp);
 }
 
 
 function closeMediaStream(stream) {
     if (!stream) {
         return;
     }
 
     // Latest spec states that MediaStream has no stop() method and instead must
     // call stop() on every MediaStreamTrack.
     if (MediaStreamTrack && MediaStreamTrack.prototype && MediaStreamTrack.prototype.stop) {
         if (stream.getTracks) {
             for (let track of stream.getTracks()) {
                 track.stop();
             }
         } else {
             for (let track of stream.getAudioTracks()) {
                 track.stop();
             }
 
             for (let track of stream.getVideoTracks()) {
                 track.stop();
             }
         }
     // Deprecated by the spec, but still in use.
     } else if (typeof stream.stop === 'function') {
         stream.stop();
     }
 }
 
 
 export default { Identity, createLocalSdp, mungeSdp, attachMediaStream, closeMediaStream };