'React. Please file an issue.',
    );
    if (__DEV__) {
      // 
      if (typeof newChildrenIterable.entries === 'function') {
        const possibleMap = (newChildrenIterable: any);
        if (possibleMap.entries === iteratorFn) {
          warning(
            didWarnAboutMaps,
            'Using Maps as children is unsupported and will likely yield ' +
              'unexpected results. Convert it to a sequence/iterable of keyed ' +
              'ReactElements instead.%s',
            getCurrentFiberStackAddendum(),
          );
          didWarnAboutMaps = true;
        }
      }
      // 
      // 
      const newChildren = iteratorFn.call(newChildrenIterable);
      if (newChildren) {
        let knownKeys = null;
        let step = newChildren.next();
        for (; !step.done; step = newChildren.next()) {
          const child = step.value;
          knownKeys = warnOnInvalidKey(child, knownKeys);
        }
      }
    }
    const newChildren = iteratorFn.call(newChildrenIterable);