code: public static RequestToken fetchData(String id, int flags, BaasHandler<JsonObject> handler){
          if(id==null) throw new IllegalArgumentException("asset id cannot be null");
          BaasBox box = BaasBox.getDefaultChecked();
          AssetDataRequest req = new AssetDataRequest(box,id,flags,handler);
          return box.submitAsync(req);
      }
docs: Asynchronously retrieves named assets data,
  If the named asset is a document, the document is retrieved
  otherwise attached data to the file are returned.
  
  @param id the name of the asset
  @param flags used for the request a bit or of {@link RequestOptions} constants
  @param handler an handler that will be handed the response
  @return a request token