code: public Observable<Page<NamespaceResourceInner>> listAsync() {
          return listWithServiceResponseAsync()
              .map(new Func1<ServiceResponse<Page<NamespaceResourceInner>>, Page<NamespaceResourceInner>>() {
                  @Override
                  public Page<NamespaceResourceInner> call(ServiceResponse<Page<NamespaceResourceInner>> response) {
                      return response.body();
                  }
              });
      }
docs: Lists all the available namespaces within the subscription irrespective of the resourceGroups.
  
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the PagedList&lt;NamespaceResourceInner&gt; object