My NetXMS server accepts traps containing nine variables, including variable "severity".

I need to set event's severity according to value of that variable.
Is there any possibility to do this (using scripts, for example)?

Something like

if ( $event->parameters[2] == "7")
{
 $event->severity = 1;
}

(this script does not work, execution error: Unknown object's attribute.
But according to wiki https://wiki.netxms.org/wiki/NXSL:Event there is the Int32 attribute named "severity" for the object "event", so why do i get this error "Unknown object's attribute"? )