title: WebRTCStats - GoogRTT and PacketsLost is null sometimes
body: <p>Just wondering why this might be the case. </p>
  
  <p>Looking over an entire media session between two WebRTC peers, it seems that some reports from the 'send' audio channel have <code>null</code> values for <code>googRtt</code> and <code>packetsLost</code>. Is there a reason for this?</p>
  
  <p>Example:</p>
  
  <pre><code>"sendAudioChannel": {
              "googCodecName": "opus",
              "googRtt": null,
              "bytesSent": 22636,
              "packetsSent": 190,
              "packetsLost": null,
              "audioInputLevel": 0,
              "googJitterReceived": null,
              "googResidualEchoLikelihood": 0,
              "googEchoCancellationReturnLoss": -100,
              "googVoiceCaptureToPacketDelayMs": 0,
              "googEchoCancellationReturnLossEnhancement": -100
            }
  </code></pre>
  
  <p>This event is from half way through the call.</p>