docs: function unset(appName, tagNames, callback) {
      if (!util.isArray(tagNames)) {
        return callback(new Error('To unset a tag pass an array of names'));
      }
  
      var keyValues = {};
      tagNames.forEach(function eachTag(tagName) {
        keyValues[tagName] = null;
      });
  
      set(appName, keyValues, callback);
    }