error in execution of calculated value script

Hi everyone
i am trying to customize an enumeration attribute named PRIORITY on the basis of another attribute named SEVERITY. the script is as follows

dojo.provide("com.example.ValueProvider");
dojo.require("com.ibm.team.workitem.api.common.WorkItemAttributes");

(function() {
var WorkItemAttributes=com.ibm.team.workitem.api.common.WorkItemAttributes;
dojo.declare("com.example.ValueProvider", null, {

        getValue: function(attribute, workItem, configuration) {

var sev = workItem.getValue("com.ibm.team.workitem.attribute.severity");
console.log("\n" +sev+"\n");
return this.valuez(sev);
},

checkforLow:function(val)
{
if((sev == "severity.literal.l1") || (sev == "severity.literal.l2") || (sev == "severity.literal.l3"))
{return true;}
else
{return false;}
},

checkforMedium:function(val)
{
if((sev == "severity.literal.l4") || (sev == "severity.literal.l5"))
{return true;}
elsel
{return false;}
},

checkforHigh:function(val)
{
if(sev == "severity.literal.l6")
{return true;}
else
{return false;}
        },
       
        valuez:function(sev)
        {
        if(checkforLow(sev))
        {
        return "Low";
        }
        else if (checkforMedium(sev))
        {
        return "Medium";
        }
        else if (checkforHigh(sev))
        {
        return "High";
        }
       
        }
    });
})();


but i can't get any effect on the rtc system. on checking log file, i got the error as :-
ERROR com.ibm.team.workitem.common   - Error invoking value provider 'AttributeCalculator' associated with the attribute 'Priority' in the project area with id '_FaqaQCNTEeik2I86tKZHPA'. You can link to the project area definition using a URL similar to https://thehostname:9443/jazz/process/project-areas/_FaqaQCNTEeik2I86tKZHPA, where the host name, port and jazz context are configured for your installation.