default groupProperties to empty object in logEvent

CHANGELOG.md

@@ -1,3 +1,6 @@
+
+* Default groupProperties to empty object in logEvent.
+
 ### 4.5.1 (November 7, 2018)
 
 * Fix error that might occur if another party defines a global variable named `Buffer` that is not actually a `Buffer`.

amplitude.js

@@ -7597,6 +7597,7 @@ AmplitudeClient.prototype._logEvent = function _logEvent(eventType, eventPropert
     apiProperties = merge_1$1(trackingOptions, apiProperties || {});
     eventProperties = eventProperties || {};
     groups = groups || {};
+    groupProperties = groupProperties || {};
     var event = {
       device_id: this.options.deviceId,
       user_id: this.options.userId,

src/amplitude-client.js

@@ -956,6 +956,7 @@ AmplitudeClient.prototype._logEvent = function _logEvent(eventType, eventPropert
     apiProperties = merge(trackingOptions, (apiProperties || {}));
     eventProperties = eventProperties || {};
     groups = groups || {};
+    groupProperties = groupProperties || {};
     var event = {
       device_id: this.options.deviceId,
       user_id: this.options.userId,