[plain java] Adding Timesheetentry to query?

I want to use Plain Java API query workitems with Timesheetentry.

I used the following source, but it not work.(error).

source:

  String strTimesheet = ModelPackage.eINSTANCE.getTimeSheetEntry().getName();
  IQueryableAttribute timesheetAttribute= queryableAttributeFactory.findAttribute(projectArea, strTimesheet, auditableClient, progressMonitor);
  AttributeExpression timesheetExpression= new AttributeExpression(timesheetAttribute, AttributeOperation.EXISTS, projectArea);
  expression.add(timesheetExpression);

I think that Timetracking(TimeSheetEntry) is not an attribute? How to do it? Could anyone help me to resolve it?