protected void saveNil(EStructuralFeature f)
protected void saveNil(EObject o, EStructuralFeature f)
  protected void saveNil(EStructuralFeature f)  {    String name = helper.getQName(f);    doc.startElement(name);    doc.addAttribute(XSI_NIL, "true");    doc.endEmptyElement();    declareXSI = true;  }