Fix NPE in Netty-mqtt client (#1398)

* Fix NPE in netty-mqtt client on puback

* Fix gateway mqtt extension configuration - filter is not required

@@ -222,6 +222,9 @@ final class MqttChannelHandler extends SimpleChannelInboundHandler<MqttMessage>
 
     private void handlePuback(MqttPubAckMessage message) {
         MqttPendingPublish pendingPublish = this.client.getPendingPublishes().get(message.variableHeader().messageId());
+        if (pendingPublish == null) {
+            return;
+        }
         pendingPublish.getFuture().setSuccess(null);
         pendingPublish.onPubackReceived();
         this.client.getPendingPublishes().remove(message.variableHeader().messageId());

@@ -261,7 +261,7 @@
                                                                                 </md-input-container>
                                                                                 <md-input-container flex="60" class="md-block" md-is-error="theForm['mqttFilterExpression' + brokerIndex + mapIndex].$touched && theForm['mqttFilterExpression' + brokerIndex + mapIndex].$invalid">
                                                                                     <label translate>extension.filter-expression</label>
-                                                                                    <input required name="mqttFilterExpression{{brokerIndex}}{{mapIndex}}" ng-model="map.converter.filterExpression">
+                                                                                    <input name="mqttFilterExpression{{brokerIndex}}{{mapIndex}}" ng-model="map.converter.filterExpression">
                                                                                     <div ng-messages="theForm['mqttFilterExpression' + brokerIndex + mapIndex].$error">
                                                                                         <div translate ng-message="required">extension.field-required</div>
                                                                                     </div>