Environment

• VerneMQ Version: 1.11.0
• OS: CentOS 8.0
• Erlang/OTP version (if building from source):
• VerneMQ configuration (vernemq.conf) or the changes from the default :
  listener.ssl.default = 0.0.0.0:8883
  listener.ssl.allowed_protocol_versions = 3,4,5
  listener.ssl.require_certificate = on
  mqtt_connect_timeout = 30000
• Cluster size/standalone:

Expected behaviour

Set

Hi,

For safety use, it's better to have null check for all variables which are used in this function.

if (!_sessionPriv.$clientAlarmList) {
    return;
}

↓

if (!_sessionPriv.$clientAlarmList
     || !_sessionPriv.$monitoredItemForAlarmList
     || !_sessionPriv.$subscriptionforAlarmList ) {
    return;
}

https://github.com/node-opcua/node-opcua/blob/master/pack