newChild,
          expirationTime,
          null,
        );
      }
      throwOnInvalidObjectType(returnFiber, newChild);
    }
    if (__DEV__) {
      if (typeof newChild === 'function') {
        warnOnFunctionType();
      }
    }
    return null;
  }
  /**
   * Warns if there is a duplicate or missing key
   */
  function warnOnInvalidKey(
    child: mixed,
    knownKeys: Set<string> | null,
  ): Set<string> | null {
    if (__DEV__) {
      if (typeof child !== 'object' || child === null) {
        return knownKeys;
      }
      switch (child.$$typeof) {
        case REACT_ELEMENT_TYPE:
        case REACT_PORTAL_TYPE:
          warnForMissingKey(child);
          const key = child.key;