docs: private static Subject setCallerSubject(Subject s) {
          Subject currentCallerSubject = null;
          SubjectManagerService sms = smServiceRef.getService();
          if (sms != null) {
              if (s == null) {
                  s = new Subject();
              }
              currentCallerSubject = sms.getCallerSubject();
              sms.setCallerSubject(s);
          }
          return currentCallerSubject;
      }