body property Null safety
The widget to show inside the NestedScrollView.
Typically this will be TabBarView.
The body is built in a context that provides a PrimaryScrollController that interacts with the NestedScrollView's scroll controller. Any ListView or other Scrollable-based widget inside the body that is intended to scroll with the NestedScrollView should therefore not be given an explicit ScrollController, instead allowing it to default to the PrimaryScrollController provided by the NestedScrollView.
final Widget body;