docs: function addType(descriptor) {
    if (!(descriptor instanceof fs.Stats)) {
      return descriptor;
    }
    [
      "isFile", "isDirectory", "isBlockDevice", "isCharacterDevice",
      "isSymbolicLink", "isFIFO", "isSocket",
    ].forEach(function(funcName) {
      if (descriptor[funcName]()) {
        descriptor[funcName] = true;
      } else {
        descriptor[funcName] = undefined;
      }
    });
    if (_.isArray(descriptor.content)) {
      descriptor.content.forEach(function(obj) {
        addType(obj);
      });
    }
    return descriptor;
  }