code: @Override
      protected Observable resumeWithFallback() {
          if (commandActions.hasFallbackAction()) {
              MetaHolder metaHolder = commandActions.getFallbackAction().getMetaHolder();
              Throwable cause = getExecutionException();
              if (cause instanceof CommandActionExecutionException) {
                  cause = cause.getCause();
              }
  
              Object[] args = createArgsForFallback(metaHolder, cause);
              try {
                  Object res = commandActions.getFallbackAction().executeWithArgs(executionType, args);
                  if (res instanceof Observable) {
                      return (Observable) res;
                  } else if (res instanceof Single) {
                      return ((Single) res).toObservable();
                  } else if (res instanceof Completable) {
                      return ((Completable) res).toObservable();
                  } else {
                      return Observable.just(res);
                  }
              } catch (Exception e) {
                  LOGGER.error(AbstractHystrixCommand.FallbackErrorMessageBuilder.create()
                          .append(commandActions.getFallbackAction(), e).build());
                  throw new FallbackInvocationException(e.getCause());
              }
          }
          return super.resumeWithFallback();
      }
docs: {@inheritDoc}.