code: public Observable<ResourceListKeysInner> listKeysAsync(String resourceGroupName, String namespaceName, String notificationHubName, String authorizationRuleName) {
          return listKeysWithServiceResponseAsync(resourceGroupName, namespaceName, notificationHubName, authorizationRuleName).map(new Func1<ServiceResponse<ResourceListKeysInner>, ResourceListKeysInner>() {
              @Override
              public ResourceListKeysInner call(ServiceResponse<ResourceListKeysInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets the Primary and Secondary ConnectionStrings to the NotificationHub.
  
  @param resourceGroupName The name of the resource group.
  @param namespaceName The namespace name.
  @param notificationHubName The notification hub name.
  @param authorizationRuleName The connection string of the NotificationHub for the specified authorizationRule.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the ResourceListKeysInner object