DragTargetLeave<T>  typedef 
    Null safety
 
Signature for when a Draggable leaves a DragTarget.
Used by DragTarget.onLeave.
Implementation
typedef DragTargetLeave<T> = void Function(T? data);Signature for when a Draggable leaves a DragTarget.
Used by DragTarget.onLeave.
typedef DragTargetLeave<T> = void Function(T? data);