code: public Observable<SubscriptionInner> getAsync(String subscriptionId) {
          return getWithServiceResponseAsync(subscriptionId).map(new Func1<ServiceResponse<SubscriptionInner>, SubscriptionInner>() {
              @Override
              public SubscriptionInner call(ServiceResponse<SubscriptionInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets details about a specified subscription.
  
  @param subscriptionId The ID of the target subscription.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the SubscriptionInner object