Fix JS error returned by callstats when no error is passed to be reported

modules/statistics/CallStats.js

@@ -241,6 +241,10 @@ CallStats.sendDominantSpeakerEvent = _try_catch(function (cs) {
  * @private
  */
 CallStats._reportEvent = function (event) {
+    if(!event) {
+        logger.warn("No event is passed!");
+        return;
+    }
     if (callStats) {
         callStats.sendFabricEvent(this.peerconnection, event, this.confID);
     } else {
@@ -302,6 +306,11 @@ function(overallFeedback, detailedFeedback) {
  * @private
  */
 CallStats._reportError = function (type, e, pc) {
+    if(!e) {//nothing to report
+        logger.warn("No error is passed!");
+        return;
+    }
+
     if (callStats) {
         callStats.reportError(pc, this.confID, type, e);
     } else {