diff --git a/.gitignore b/.gitignore
index f1138e7..0d2b1fb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
+.idea/
 node_modules
 .npm
 target
diff --git a/src/paho-mqtt.js b/src/paho-mqtt.js
index 9ca3d37..fd14176 100644
--- a/src/paho-mqtt.js
+++ b/src/paho-mqtt.js
@@ -1809,7 +1809,7 @@ function onMessageArrived(message) {
 				"onConnected":{
 					get: function() { return client.onConnected; },
 					set: function(newOnConnected) {
-						if (typeof newOnConnected === "function")
+						if (newOnConnected === null || typeof newOnConnected === "function")
 							client.onConnected = newOnConnected;
 						else
 							throw new Error(format(ERROR.INVALID_TYPE, [typeof newOnConnected, "onConnected"]));
@@ -1830,7 +1830,7 @@ function onMessageArrived(message) {
 				"onConnectionLost":{
 					get: function() { return client.onConnectionLost; },
 					set: function(newOnConnectionLost) {
-						if (typeof newOnConnectionLost === "function")
+						if (newOnConnectionLost === null || typeof newOnConnectionLost === "function")
 							client.onConnectionLost = newOnConnectionLost;
 						else
 							throw new Error(format(ERROR.INVALID_TYPE, [typeof newOnConnectionLost, "onConnectionLost"]));
@@ -1839,7 +1839,7 @@ function onMessageArrived(message) {
 				"onMessageDelivered":{
 					get: function() { return client.onMessageDelivered; },
 					set: function(newOnMessageDelivered) {
-						if (typeof newOnMessageDelivered === "function")
+						if (newOnMessageDelivered === null || typeof newOnMessageDelivered === "function")
 							client.onMessageDelivered = newOnMessageDelivered;
 						else
 							throw new Error(format(ERROR.INVALID_TYPE, [typeof newOnMessageDelivered, "onMessageDelivered"]));
@@ -1848,7 +1848,7 @@ function onMessageArrived(message) {
 				"onMessageArrived":{
 					get: function() { return client.onMessageArrived; },
 					set: function(newOnMessageArrived) {
-						if (typeof newOnMessageArrived === "function")
+						if (newOnMessageArrived === null || typeof newOnMessageArrived === "function")
 							client.onMessageArrived = newOnMessageArrived;
 						else
 							throw new Error(format(ERROR.INVALID_TYPE, [typeof newOnMessageArrived, "onMessageArrived"]));
@@ -1857,7 +1857,7 @@ function onMessageArrived(message) {
 				"trace":{
 					get: function() { return client.traceFunction; },
 					set: function(trace) {
-						if(typeof trace === "function"){
+						if (trace === null || typeof trace === "function"){
 							client.traceFunction = trace;
 						}else{
 							throw new Error(format(ERROR.INVALID_TYPE, [typeof trace, "onTrace"]));