anchor.diff:    const NavigationRailDestination({
       required this.icon,
       Widget? selectedIcon,
  -    this.label,
  +    required this.label,
       this.padding,
     }) : selectedIcon = selectedIcon ?? icon,
  -       assert(icon != null);
  +       assert(icon != null),
  +       assert(label != null);
   
     /// The icon of the destination.
     ///
  
positive.code:                           extendedTransitionAnimation: _extendedAnimation,
                            selected: widget.selectedIndex == i,
                            icon: widget.selectedIndex == i ? widget.destinations[i].selectedIcon : widget.destinations[i].icon,
                            label: widget.destinations[i].label!,
                            destinationAnimation: _destinationAnimations[i],
                            labelType: labelType,
                            iconTheme: widget.selectedIndex == i ? selectedIconTheme : unselectedIconTheme,
  
negative.code:   /// [NavigationRail.labelType] is [NavigationRailLabelType.none], the label is
    /// still used for semantics, and may still be used if
    /// [NavigationRail.extended] is true.
    final Widget label;
  
    /// The amount of space to inset the destination item.
    final EdgeInsetsGeometry? padding;
  