Never mind got it working. Thank you very much for your help.

Here is the final script:

(function executeRule(current, previous /*null when async*/) {

   gs.log("AV Location Script - Start");

   var desc = current.description;

   var pos = desc.search('Context:');

   var contextID = desc.substring(pos+8);

   contextID = contextID.trim();


   var locationRec = new GlideRecord('cmn_location');

   locationRec.addQuery('u_context_id', contextID);

   locationRec.query();

   if (locationRec.next()) {

   current.location = locationRec.sys_id;

   current.company = locationRec.company.sys_id;

   }

   else {

   current.work_notes = '<br>WARNING - THIS ALERT DOES NOT HAVE A CORRESPONDING SITE IN SERVICENOW - PLEASE INFORM THE LOCAL SERVICENOW ADMIN.';

   }

   //gs.log("AV Location Script - End");

})(current, previous);