code: function uniquenessValidator(values) {
    if (values.presentAuthors) {
      values = values.presentAuthors;
    }
    values.sort();
  
    for (var i = 0; i < values.length - 1; i++) {
      if (values[i] === values[i+1]) {
        // can throw error or return false
        // error allows supplying more detail
        throw new Error('Duplicate value [' + values[i] + '] found in Room.presentAuthors');
      }
    }
  
    return true;
  }
docs: are all values unique?