Environment

• VerneMQ Version: using docker image vernemq/vernemq:latest
• OS: Debian 9
• Erlang/OTP version (if building from source):
• Cluster size/standalone: standalone
• VerneMQ configuration (vernemq.conf) or the changes from the default

accept_eula=yes
allow_anonymous=off
log.console=console
log.console.level=debug
plugins.vmq_acl=off
plugins.vmq_diversity=on
plugins.v

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