message: Field: mark id as optional in propTypes
diff: @@ -32,7 +32,7 @@ function getId() {
  export default class Field extends React.PureComponent {
  static propTypes = {
  // The field's ID, which binds the input and label together. Immutable.
  - id: PropTypes.string.isRequired,
  + id: PropTypes.string,
  // The element to create. Defaults to "input".
  // To define options for a select, use <Field><option ... /></Field>
  element: PropTypes.oneOf(["input", "select", "textarea"]),
  