code: function toFiles(app, options) {
    let opts = Object.assign({ collection: null }, options);
    let name = opts.collection;
    let collection = app.collections ? name && app[name] : app;
    let view;
  
    if (!collection && name) {
      collection = app.create(name, opts);
    }
  
    return utils.through.obj(async (file, enc, next) => {
      if (!app.File.isFile(file)) {
        file = app.file(file.path, file);
      }
  
      if (file.isNull()) {
        next(null, file);
        return;
      }
  
      if (collection && isCollection(collection)) {
        try {
          view = await collection.set(file.path, file);
        } catch (err) {
          next(err);
          return;
        }
        next(null, view);
        return;
      }
  
      view = !app.File.isFile(file) ? app.file(file.path, file) : file;
  
      app.handle('onLoad', view)
        .then(() => next(null, view))
        .catch(next);
    });
  }
docs: Make sure vinyl files are assemble files, and add
  them to a collection, if specified.