[Cupertino] Fix warnings

Runtime/cupertino/button.cs

             BorderRadius borderRadius = null,
             bool filled = false
         ) : base(key: key) {
-            D.assert(pressedOpacity == null || (pressedOpacity >= 0.0 && pressedOpacity <= 1.0));
+            D.assert(pressedOpacity >= 0.0 && pressedOpacity <= 1.0);
             this._filled = filled;
             this.child = child;
             this.onPressed = onPressed;
             float pressedOpacity = 0.1f,
             BorderRadius borderRadius = null
         ) {
-            D.assert(pressedOpacity == null || (pressedOpacity >= 0.0 && pressedOpacity <= 1.0));
+            D.assert(pressedOpacity >= 0.0 && pressedOpacity <= 1.0);
             return new CupertinoButton(
                 key: key,
                 color: null,
                         }
                     },
                 child: new ConstrainedBox(
-                    constraints: this.widget.minSize == null
-                        ? new BoxConstraints()
-                        : new BoxConstraints(
-                            minWidth: this.widget.minSize,
-                            minHeight: this.widget.minSize
-                        ),
+                    constraints: new BoxConstraints(
+                        minWidth: this.widget.minSize,
+                        minHeight: this.widget.minSize
+                    ),
                     child: new FadeTransition(
                         opacity: this._opacityAnimation,
                         child: new DecoratedBox(

Runtime/cupertino/nav_bar.cs

             BuildContext toHeroContext
         ) => {
             D.assert(animation != null);
-            D.assert(flightDirection != null);
+
             D.assert(fromHeroContext != null);
             D.assert(toHeroContext != null);
             D.assert(fromHeroContext.widget is Hero);
                         bottomNavBar: fromNavBar,
                         topNavBar: toNavBar
                     );
-                    break;
                 case HeroFlightDirection.pop:
                     return new _NavigationBarTransition(
                         animation: animation,
                 new Builder(
                     builder: (BuildContext _context) => {
                         return new Hero(
-                            tag: this.widget.heroTag == NavBarUtils._defaultHeroTag
+                            tag: this.widget.heroTag as _HeroTag == NavBarUtils._defaultHeroTag
                                 ? new _HeroTag(Navigator.of(_context))
                                 : this.widget.heroTag,
                             createRectTween: NavBarUtils._linearTranslateWithLargestRectSizeTween,
             bool transitionBetweenRoutes = true,
             object heroTag = null
         ) : base(key: key) {
-            D.assert(automaticallyImplyLeading != null);
-            D.assert(automaticallyImplyTitle != null);
             D.assert(
                 automaticallyImplyTitle == true || largeTitle != null,
                 () => "No largeTitle has been provided but automaticallyImplyTitle is also " +
             float persistentHeight,
             bool alwaysShowMiddle
         ) {
-            D.assert(this.persistentHeight != null);
-            D.assert(this.alwaysShowMiddle != null);
-            D.assert(this.transitionBetweenRoutes != null);
             this.keys = keys;
             this.components = components;
             this.userMiddle = userMiddle;
             }
 
             return new Hero(
-                tag: this.heroTag == NavBarUtils._defaultHeroTag
+                tag: this.heroTag as _HeroTag == NavBarUtils._defaultHeroTag
                     ? new _HeroTag(Navigator.of(context))
                     : this.heroTag,
                 createRectTween: NavBarUtils._linearTranslateWithLargestRectSizeTween,
                     style: CupertinoTheme.of(context).textTheme.navTitleTextStyle,
                     child: middle
                 );
-                middle = this.middleVisible == null
-                    ? middle
-                    : new AnimatedOpacity(
-                        opacity: this.middleVisible ? 1.0f : 0.0f,
-                        duration: NavBarUtils._kNavBarTitleFadeDuration,
-                        child: middle
-                    );
+                middle = new AnimatedOpacity(
+                    opacity: this.middleVisible ? 1.0f : 0.0f,
+                    duration: NavBarUtils._kNavBarTitleFadeDuration,
+                    child: middle
+                );
             }
 
             Widget leading = this.components.leading;
             _TransitionableNavigationBar topNavBar,
             _TransitionableNavigationBar bottomNavBar
         ) {
+            this.animation = animation;
+            this.topNavBar = topNavBar;
+            this.bottomNavBar = bottomNavBar;
             this.heightTween = new FloatTween(
                 begin: this.bottomNavBar.renderBox.size.height,
                 end: this.topNavBar.renderBox.size.height
             _TransitionableNavigationBar topNavBar,
             TextDirection directionality
         ) {
+            this.animation = animation;
             this.bottomComponents = bottomNavBar.componentsKeys;
             this.topComponents = topNavBar.componentsKeys;
             this.bottomNavBarBox = bottomNavBar.renderBox;

Runtime/cupertino/page_scaffold.cs

             bool resizeToAvoidBottomInset = true
         ) : base(key: key) {
             D.assert(child != null);
-            D.assert(resizeToAvoidBottomInset != null);
 
             this.child = child;
             this.navigationBar = navigationBar;

Runtime/cupertino/route.cs

             _CupertinoEdgeShadowDecoration b,
             float t
         ) {
-            D.assert(t != null);
             if (a == null && b == null) {
                 return null;
             }
 
         public override BoxPainter createBoxPainter(VoidCallback onChanged = null) {
             return new _CupertinoEdgeShadowPainter(this, onChanged);
+        }
+
+        public override int GetHashCode() {
+            return this.edgeGradient.GetHashCode();
         }
 
         public bool Equals(_CupertinoEdgeShadowDecoration other) {
         ) :
             base(settings: settings, fullscreenDialog: fullscreenDialog) {
             D.assert(builder != null);
-            D.assert(maintainState != null);
-            D.assert(fullscreenDialog != null);
             D.assert(this.opaque);
             this.builder = builder;
             this.title = title;
             return buildPageTransitions(this, context, animation, secondaryAnimation, child);
         }
 
-        public string debugLabel {
+        public new string debugLabel {
             get { return $"{base.debugLabel}(${this.settings.name})"; }
         }
     }
             bool linearTransition,
             Key key = null
         ) : base(key: key) {
-            D.assert(linearTransition != null);
             this._primaryPositionAnimation =
                 (linearTransition
                     ? primaryRouteAnimation
             get { return CupertinoRouteUtils._kModalPopupTransitionDuration; }
         }
 
-        Animation<float> _animation;
+        new Animation<float> _animation;
-
 
         public override Animation<float> createAnimation() {
             D.assert(this._animation == null);

Runtime/cupertino/slider.cs

         ) : base(key: key) {
             D.assert(value != null);
             D.assert(onChanged != null);
-            D.assert(min != null);
-            D.assert(max != null);
             D.assert(value >= min && value <= max);
             D.assert(divisions == null || divisions > 0);
             this.value = value.Value;
             TickerProvider vsync = null
         ) : base(additionalConstraints: BoxConstraints.tightFor(width: SliderUtils._kSliderWidth,
             height: SliderUtils._kSliderHeight)) {
-            D.assert(value != null && value >= 0.0f && value <= 1.0f);
+            D.assert(value >= 0.0f && value <= 1.0f);
             this._value = value;
             this._divisions = divisions;
             this._activeColor = activeColor;
         public float value {
             get { return this._value; }
             set {
-                D.assert(value != null && value >= 0.0f && value <= 1.0f);
+                D.assert(value >= 0.0f && value <= 1.0f);
                 if (value == this._value) {
                     return;
                 }

Runtime/cupertino/switch.cs

             Key key = null,
             Color activeColor = null,
             DragStartBehavior dragStartBehavior = DragStartBehavior.start
-        ) :
-            base(key: key) {
-            D.assert(value != null);
-            D.assert(dragStartBehavior != null);
-
+        ) : base(key: key) {
             this.value = value;
             this.onChanged = onChanged;
             this.activeColor = activeColor;
             width: CupertinoSwitchUtils._kSwitchWidth,
             height: CupertinoSwitchUtils._kSwitchHeight)
         ) {
-            D.assert(value != null);
             D.assert(activeColor != null);
             D.assert(vsync != null);
             this._value = value;
         public bool value {
             get { return this._value; }
             set {
-                D.assert(value != null);
                 if (value == this._value) {
                     return;
                 }
         public TextDirection textDirection {
             get { return this._textDirection; }
             set {
-                D.assert(value != null);
                 if (this._textDirection == value) {
                     return;
                 }
         public DragStartBehavior dragStartBehavior {
             get { return this._drag.dragStartBehavior; }
             set {
-                D.assert(value != null);
                 if (this._drag.dragStartBehavior == value) {
                     return;
                 }

Runtime/cupertino/tab_scaffold.cs

             int tabNumber,
             IndexedWidgetBuilder tabBuilder
         ) {
-            D.assert(currentTabIndex != null);
-            D.assert(tabNumber != null && tabNumber > 0);
+            D.assert(tabNumber > 0);
+            this.currentTabIndex = currentTabIndex;
+            this.tabNumber = tabNumber;
+            this.tabBuilder = tabBuilder;
         }
 
         public readonly int currentTabIndex;