code: @NonNull
      public ObservableDataBuilder<T> available(@Nullable Observable<Integer> available) {
          mAvailable = available;
          return this;
      }
docs: The {@link Data#available()} property will match the emissions of this observable, starting with
  {@code Integer.MAX_VALUE} until the first emission.
  <p>
  If not specified, the resulting data will assume there are no more elements available after the first emission
  of any of the content observables.
  @see #contents(Observable)
  @see #prepends(Observable)
  @see #appends(Observable)