Problem in accessing enumeration in work item using client java API

HI All,
I am trying to get value of enumeration literal using java API. I referred this link to access enumeration values using java API.
but when I use IAttribute to fetch required attribute I am getting Null pointer exception.
IAttribute someAttribute= workItemClient.findAttribute(projectareahandle, "severity", null);
value of someAttribute variable in null.

IAttribute someAttribute= workItemClient.findAttribute(projectareahandle, "com.ibm.team.workitem.attribute.severity", null);
this code snippet also return value of someAttribute as null. Therefore further part of code is not executed.
Is there any other way to fetch attribute of type enumeration. Or am I doing something wrong here,?

following is complete code snippet of my program

IProjectAreaHandle projectareahandle = projectArea.getProjectArea();
        IWorkItemClient workItemClient = (IWorkItemClient) teamRepository.getClientLibrary(IWorkItemClient.class);
        IWorkItem work = workItemClient.findWorkItemById(id, IWorkItem.FULL_PROFILE, null);
        IWorkItem workcopy = (IWorkItem)work.getWorkingCopy();
        IAttribute someAttribute= workItemClient.findAttribute(projectareahandle, "severity", null);
       
        Object value = workcopy.getValue(someAttribute);
       
        if(value instanceof Identifier)
        {
            Identifier literalID = (Identifier) value;
            IEnumeration enumeration = workItemClient.resolveEnumeration(someAttribute, null);
            List literals = enumeration.getEnumerationLiterals();
            for (Iterator iterator = literals.iterator(); iterator.hasNext();)
            {
                ILiteral iLiteral = (ILiteral) iterator.next();
                if (iLiteral.getIdentifier2().equals(literalID))
                {
                    String displayvalue = iLiteral.getName();
                    System.out.println("its value is "+displayvalue);
                }
            }
        }

in someAttribute value fetched is null therefore further part is not executed.