message: Appease the linter
  This checks `onValidate` in `render` to make the linter happy.
diff: @@ -95,10 +95,13 @@ export default class Field extends React.PureComponent {
  prefixContainer = <span className="mx_Field_prefix">{prefix}</span>;
  }
  - const validClass = classNames({
  + let validClass;
  + if (onValidate) {
  + validClass = classNames({
  mx_Field_valid: this.state.valid === true,
  mx_Field_invalid: this.state.valid === false,
  });
  + }
  const fieldClasses = classNames("mx_Field", `mx_Field_${inputElement}`, {
  // If we have a prefix element, leave the label always at the top left and
  