How to query a work item based on a custom attribute?

How to query a work item based on a custom attribute? I'm trying the following code, but always getting null for queryableCustom in the code below.

IAuditableClient auditableClient = (IAuditableClient) teamRepository

				.getClientLibrary(IAuditableClient.class);

		IQueryableAttribute queryableCustom = QueryableAttributes.getFactory(IWorkItem.ITEM_TYPE)

				.findAttribute(processArea, "cmvc_name", auditableClient, monitor);

		System.out.println("queryableCustom="+queryableCustom);

		Expression attributeExpression = new AttributeExpression(queryableCustom,

				AttributeOperation.EQUALS, defectName);

		System.out.println("attributeExpression="+attributeExpression);

		IQueryClient queryClient = (IQueryClient) teamRepository

				.getClientLibrary(IQueryClient.class);

		IQueryResult<IResolvedResult<IWorkItem>> result = queryClient.getResolvedExpressionResults(

				processArea, attributeExpression, IWorkItem.FULL_PROFILE);

		if (result.hasNext(monitor)) {

			IResolvedResult<IWorkItem> resolved = result.next(monitor);

			System.out.println("Name="+resolved.getItem().getHTMLSummary());

			return resolved.getItem();

		}