code: function discoverKey(arr, discoverableKeys, defaultKey) {
    if (arr.length === 0) return defaultKey;
    if (arr.length === 1) return arr[0];
    for (var i = 0; i < arr.length; i++) {
      if (discoverableKeys[arr[i]]) return arr[i];
    }
    return defaultKey;
  }
docs: Auto-discover the plural key
  
  @param {Array} keys
  @param {Object} discoverableKeys
  @param {String} defaultKey
  @return {String}