code: public Observable<ComapiResult<Void>> endSession() {
          if (isSessionValid()) {
              return wrapObservable(sessionController.endSession().map(mapToComapiResult()));
          } else {
              //return Observable.onError(getSessionStateErrorDescription());
              return Observable.just(null);
          }
      }
docs: Ends currently active session.
  
  @return Observable to end current session.