Occurs in Fiber with multiple instances of the React package (which can't share current owner).
* object keys are not valid. This allows us to keep track of children between
   * updates.
   */
  var ownerHasKeyUseWarning = {};
  var warnForMissingKey = (child: mixed) => {
    if (child === null || typeof child !== 'object') {
      return;
    }
    if (!child._store || child._store.validated || child.key != null) {
      return;
    }
    invariant(
      typeof child._store === 'object',
      'React Component in warnForMissingKey should have a _store',
    );
    child._store.validated = true;
    var currentComponentErrorInfo =
      'Each child in an array or iterator should have a unique ' +
      '"key" prop. See https://fb.me/react-warning-keys for ' +
      'more information.' +
      (getCurrentFiberStackAddendum() || '');
    if (ownerHasKeyUseWarning[currentComponentErrorInfo]) {
      return;
    }
    ownerHasKeyUseWarning[currentComponentErrorInfo] = true;
    warning(
      false,
      'Each child in an array or iterator should have a unique ' +
        '"key" prop. See https://fb.me/react-warning-keys for ' +
        'more information.%s',