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