Why when creating a Consumer, an optional child is asked? When is it used?

[stephane-archer]

Why when creating a Consumer, an optional child is asked? When is it used? The builder is what decides what is shown from my understanding.

(new) Consumer<VideoCodecChangeNotifier> Consumer({
  Key? key,
  required Widget Function(BuildContext, VideoCodecChangeNotifier, Widget?) builder,
  Widget? child,
})