diff --git a/CHANGELOG.md b/CHANGELOG.md
index a58321e51..f97a25f4f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 # CHANGELOG
 
 ## [next]
+ - Code improvements and preparing APIs to null-safety
  - BaseComponent removes children marked as shouldRemove during update
  - Use `find` instead of `globstar` pattern in `scripts/lint.sh` as the later isn't enabled by default in bash
  - Fixes aseprite constructor bug
diff --git a/doc/examples/effects/infinite_effects/lib/main.dart b/doc/examples/effects/infinite_effects/lib/main.dart
index 2ede7700e..ffa835f97 100644
--- a/doc/examples/effects/infinite_effects/lib/main.dart
+++ b/doc/examples/effects/infinite_effects/lib/main.dart
@@ -21,18 +21,19 @@ void main() async {
   );
 }
 
+const green = Color(0xAA338833);
+const red = Color(0xAA883333);
+const orange = Color(0xAABB6633);
+
 class MyGame extends BaseGame with TapDetector {
   Square greenSquare;
   Square redSquare;
   Square orangeSquare;
 
-  MyGame() {
-    final green = Paint()..color = const Color(0xAA338833);
-    final red = Paint()..color = const Color(0xAA883333);
-    final orange = Paint()..color = const Color(0xAABB6633);
-    greenSquare = Square(green, Vector2.all(100));
-    redSquare = Square(red, Vector2.all(200));
-    orangeSquare = Square(orange, Vector2(200, 400));
+  MyGame()
+      : greenSquare = Square(Paint()..color = green, Vector2.all(100)),
+        redSquare = Square(Paint()..color = red, Vector2.all(200)),
+        orangeSquare = Square(Paint()..color = orange, Vector2(200, 400)) {
     add(greenSquare);
     add(redSquare);
     add(orangeSquare);
diff --git a/doc/examples/gestures/lib/main_multitap_advanced.dart b/doc/examples/gestures/lib/main_multitap_advanced.dart
index 7c1aa2cd4..e37deb9a9 100644
--- a/doc/examples/gestures/lib/main_multitap_advanced.dart
+++ b/doc/examples/gestures/lib/main_multitap_advanced.dart
@@ -74,12 +74,14 @@ class MyGame extends BaseGame
   }
 
   void onPanEnd(DragEndDetails details) {
-    _panRect = Rect.fromLTRB(
-      _start.dx,
-      _start.dy,
-      _end.dx,
-      _end.dy,
-    );
+    if (_start != null && _end != null) {
+      _panRect = Rect.fromLTRB(
+        _start.dx,
+        _start.dy,
+        _end.dx,
+        _end.dy,
+      );
+    }
   }
 
   @override
diff --git a/doc/examples/joystick/lib/player.dart b/doc/examples/joystick/lib/player.dart
index 75a3a7aad..26620a45f 100644
--- a/doc/examples/joystick/lib/player.dart
+++ b/doc/examples/joystick/lib/player.dart
@@ -25,14 +25,15 @@ class Player extends Component implements JoystickListener {
 
   @override
   void render(Canvas canvas) {
-    if (_rect != null) {
-      canvas.save();
-      canvas.translate(_rect.center.dx, _rect.center.dy);
-      canvas.rotate(radAngle == 0.0 ? 0.0 : radAngle + (pi / 2));
-      canvas.translate(-_rect.center.dx, -_rect.center.dy);
-      canvas.drawRect(_rect, _paint);
-      canvas.restore();
+    if (_rect == null) {
+      return;
     }
+    canvas.save();
+    canvas.translate(_rect.center.dx, _rect.center.dy);
+    canvas.rotate(radAngle == 0.0 ? 0.0 : radAngle + (pi / 2));
+    canvas.translate(-_rect.center.dx, -_rect.center.dy);
+    canvas.drawRect(_rect, _paint);
+    canvas.restore();
   }
 
   @override
@@ -79,12 +80,15 @@ class Player extends Component implements JoystickListener {
     final double nextX = (currentSpeed * dtUpdate) * cos(radAngle);
     final double nextY = (currentSpeed * dtUpdate) * sin(radAngle);
 
+    if (_rect == null) {
+      return;
+    }
+
     final Offset diffBase = Offset(
           _rect.center.dx + nextX,
           _rect.center.dy + nextY,
         ) -
         _rect.center;
-
     _rect = _rect.shift(diffBase);
   }
 }
diff --git a/doc/examples/render_flip/lib/main.dart b/doc/examples/render_flip/lib/main.dart
index 55b462a4d..12b68267e 100644
--- a/doc/examples/render_flip/lib/main.dart
+++ b/doc/examples/render_flip/lib/main.dart
@@ -16,8 +16,6 @@ void main() async {
 }
 
 class MyGame extends BaseGame {
-  SpriteAnimation animation;
-
   @override
   Future<void> onLoad() async {
     final image = await images.load('chopper.png');
diff --git a/doc/examples/widgets/lib/main.dart b/doc/examples/widgets/lib/main.dart
index 70d240676..0b14a5f32 100644
--- a/doc/examples/widgets/lib/main.dart
+++ b/doc/examples/widgets/lib/main.dart
@@ -108,8 +108,9 @@ void main() async {
           child: SpriteWidget(
             sprite: shieldSprite,
             anchor: parseAnchor(
-              ctx.listProperty('anchor', 'Anchor.center', anchorOptions),
-            ),
+                  ctx.listProperty('anchor', 'Anchor.center', anchorOptions),
+                ) ??
+                Anchor.topLeft,
           ),
         ),
       );
@@ -134,8 +135,9 @@ void main() async {
             animation: _animation,
             playing: ctx.boolProperty('playing', true),
             anchor: parseAnchor(
-              ctx.listProperty('anchor', 'Anchor.center', anchorOptions),
-            ),
+                  ctx.listProperty('anchor', 'Anchor.center', anchorOptions),
+                ) ??
+                Anchor.topLeft,
           ),
         ),
       );
diff --git a/lib/components/joystick/joystick_action.dart b/lib/components/joystick/joystick_action.dart
index 08217f0f3..fa449be99 100644
--- a/lib/components/joystick/joystick_action.dart
+++ b/lib/components/joystick/joystick_action.dart
@@ -34,11 +34,11 @@ class JoystickAction {
   bool _dragging = false;
   Sprite _spriteAction;
   Offset _dragPosition;
-  Paint _paintBackground;
-  Paint _paintAction;
-  Paint _paintActionPressed;
+  final Paint _paintBackground;
+  final Paint _paintAction;
+  final Paint _paintActionPressed;
   JoystickController _joystickController;
-  double _sizeBackgroundDirection;
+  final double _sizeBackgroundDirection;
   DragEvent _currentDragEvent;
   double _tileSize;
 
@@ -55,9 +55,17 @@ class JoystickAction {
     this.align = JoystickActionAlign.BOTTOM_RIGHT,
     this.opacityBackground = 0.5,
     this.opacityKnob = 0.8,
-  }) {
-    _spriteAction = sprite;
-    _sizeBackgroundDirection = sizeFactorBackgroundDirection * size;
+  })  : _spriteAction = sprite,
+        _sizeBackgroundDirection = sizeFactorBackgroundDirection * size,
+        _paintBackground = Paint()
+          ..color = color.withOpacity(opacityBackground)
+          ..style = PaintingStyle.fill,
+        _paintAction = Paint()
+          ..color = color.withOpacity(opacityKnob)
+          ..style = PaintingStyle.fill,
+        _paintActionPressed = Paint()
+          ..color = color.withOpacity(opacityBackground)
+          ..style = PaintingStyle.fill {
     _tileSize = _sizeBackgroundDirection / 2;
   }
 
@@ -91,25 +99,6 @@ class JoystickAction {
       center: Offset(dx, dy),
       radius: _sizeBackgroundDirection / 2,
     );
-
-    if (spriteBackgroundDirection == null) {
-      _paintBackground = Paint()
-        ..color = color.withOpacity(opacityBackground)
-        ..style = PaintingStyle.fill;
-    }
-
-    if (sprite == null) {
-      _paintAction = Paint()
-        ..color = color.withOpacity(opacityKnob)
-        ..style = PaintingStyle.fill;
-    }
-
-    if (spritePressed == null) {
-      _paintActionPressed = Paint()
-        ..color = color.withOpacity(opacityBackground)
-        ..style = PaintingStyle.fill;
-    }
-
     _dragPosition = _rectAction.center;
   }
 
@@ -128,7 +117,7 @@ class JoystickAction {
   }
 
   void update(double dt) {
-    if (_dragging) {
+    if (_rectBackgroundDirection != null && _dragging) {
       final double _radAngle = atan2(
         _dragPosition.dy - _rectBackgroundDirection.center.dy,
         _dragPosition.dx - _rectBackgroundDirection.center.dx,
@@ -149,13 +138,15 @@ class JoystickAction {
       final double nextY = dist * sin(_radAngle);
       final Offset nextPoint = Offset(nextX, nextY);
 
-      final Offset diff = Offset(
-            _rectBackgroundDirection.center.dx + nextPoint.dx,
-            _rectBackgroundDirection.center.dy + nextPoint.dy,
-          ) -
-          _rectAction.center;
+      if (_rectAction != null) {
+        final Offset diff = Offset(
+              _rectBackgroundDirection.center.dx + nextPoint.dx,
+              _rectBackgroundDirection.center.dy + nextPoint.dy,
+            ) -
+            _rectAction.center;
 
-      _rectAction = _rectAction.shift(diff);
+        _rectAction = _rectAction.shift(diff);
+      }
 
       final double _intensity = dist / _tileSize;
 
@@ -176,24 +167,26 @@ class JoystickAction {
   }
 
   void onReceiveDrag(DragEvent event) {
-    if (!_dragging && (_rectAction?.contains(event.initialPosition) ?? false)) {
-      if (enableDirection) {
-        _dragPosition = event.initialPosition;
-        _dragging = true;
-      }
-      _joystickController.joystickAction(
-        JoystickActionEvent(
-          id: actionId,
-          event: ActionEvent.DOWN,
-        ),
-      );
-      tapDown();
-      _currentDragEvent = event;
-      _currentDragEvent
-        ..onUpdate = onPanUpdate
-        ..onEnd = onPanEnd
-        ..onCancel = onPanCancel;
+    if (_dragging || !(_rectAction?.contains(event.initialPosition) ?? false)) {
+      return;
     }
+
+    if (enableDirection) {
+      _dragPosition = event.initialPosition;
+      _dragging = true;
+    }
+    _joystickController.joystickAction(
+      JoystickActionEvent(
+        id: actionId,
+        event: ActionEvent.DOWN,
+      ),
+    );
+    tapDown();
+    _currentDragEvent = event;
+    _currentDragEvent
+      ..onUpdate = onPanUpdate
+      ..onEnd = onPanEnd
+      ..onCancel = onPanCancel;
   }
 
   void tapDown() {
diff --git a/lib/components/joystick/joystick_utils.dart b/lib/components/joystick/joystick_utils.dart
index 75c94b702..c29720657 100644
--- a/lib/components/joystick/joystick_utils.dart
+++ b/lib/components/joystick/joystick_utils.dart
@@ -11,6 +11,8 @@ class JoystickUtils {
     }
 
     if (sprite == null) {
+      assert(paint != null, '`paint` must not be `null` if `sprite` is `null`');
+
       final double radius = rect.width / 2;
       c.drawCircle(
         Offset(rect.left + radius, rect.top + radius),
diff --git a/lib/components/sprite_component.dart b/lib/components/sprite_component.dart
index 0e8f98846..adaf9916f 100644
--- a/lib/components/sprite_component.dart
+++ b/lib/components/sprite_component.dart
@@ -34,7 +34,7 @@ class SpriteComponent extends PositionComponent {
   @override
   void render(Canvas canvas) {
     super.render(canvas);
-    sprite.render(
+    sprite?.render(
       canvas,
       size: size,
       overridePaint: overridePaint,
diff --git a/lib/components/text_box_component.dart b/lib/components/text_box_component.dart
index 514f5389e..b0ee09861 100644
--- a/lib/components/text_box_component.dart
+++ b/lib/components/text_box_component.dart
@@ -28,11 +28,11 @@ class TextBoxConfig {
 class TextBoxComponent extends PositionComponent {
   static final Paint _imagePaint = BasicPalette.white.paint
     ..filterQuality = FilterQuality.high;
-  Vector2 _gameSize;
+  Vector2 _gameSize = Vector2.zero();
 
-  String _text;
-  TextConfig _config;
-  TextBoxConfig _boxConfig;
+  final String _text;
+  final TextConfig _config;
+  final TextBoxConfig _boxConfig;
 
   List<String> _lines;
   double _maxLineWidth = 0.0;
@@ -53,15 +53,15 @@ class TextBoxComponent extends PositionComponent {
     String text, {
     TextConfig config,
     TextBoxConfig boxConfig,
-  }) {
-    _boxConfig = boxConfig ?? TextBoxConfig();
-    _config = config ?? TextConfig();
-    _text = text;
+  })  : _text = text,
+        _boxConfig = boxConfig ?? TextBoxConfig(),
+        _config = config ?? TextConfig() {
     _lines = [];
+    double lineHeight;
     text.split(' ').forEach((word) {
       final possibleLine = _lines.isEmpty ? word : _lines.last + ' ' + word;
       final painter = _config.toTextPainter(possibleLine);
-      _lineHeight ??= painter.height;
+      lineHeight ??= painter.height;
       if (painter.width <=
           _boxConfig.maxWidth - _boxConfig.margins.horizontal) {
         if (_lines.isNotEmpty) {
@@ -76,6 +76,7 @@ class TextBoxComponent extends PositionComponent {
       }
     });
     _totalLines = _lines.length;
+    _lineHeight = lineHeight ?? 0.0;
   }
 
   void _updateMaxWidth(double w) {
diff --git a/lib/components/text_component.dart b/lib/components/text_component.dart
index 3db84da42..15b19c0c4 100644
--- a/lib/components/text_component.dart
+++ b/lib/components/text_component.dart
@@ -28,8 +28,8 @@ class TextComponent extends PositionComponent {
     _updateBox();
   }
 
-  TextComponent(this._text, {TextConfig config}) {
-    _config = config ?? TextConfig();
+  TextComponent(this._text, {TextConfig config})
+      : _config = config ?? TextConfig() {
     _updateBox();
   }
 
diff --git a/lib/effects/combined_effect.dart b/lib/effects/combined_effect.dart
index 75715da4a..a59fc8ed6 100644
--- a/lib/effects/combined_effect.dart
+++ b/lib/effects/combined_effect.dart
@@ -47,8 +47,10 @@ class CombinedEffect extends PositionComponentEffect {
           effect.originalAngle != effect.endAngle ? effect.endAngle : endAngle;
       endSize =
           effect.originalSize != effect.endSize ? effect.endSize : endSize;
-      peakTime = max(peakTime ?? 0,
-          effect.iterationTime + offset * effects.indexOf(effect));
+      peakTime = max(
+        peakTime,
+        effect.iterationTime + offset * effects.indexOf(effect),
+      );
     });
     if (isAlternating) {
       endPosition = originalPosition;
diff --git a/lib/effects/effects.dart b/lib/effects/effects.dart
index 048497270..64be33d3a 100644
--- a/lib/effects/effects.dart
+++ b/lib/effects/effects.dart
@@ -30,8 +30,8 @@ abstract class ComponentEffect<T extends BaseComponent> {
   final bool _initialIsInfinite;
   final bool _initialIsAlternating;
   double percentage;
-  double curveProgress;
-  double peakTime;
+  double curveProgress = 0.0;
+  double peakTime = 0.0;
   double currentTime = 0.0;
   double driftTime = 0.0;
   int curveDirection = 1;
@@ -43,13 +43,12 @@ abstract class ComponentEffect<T extends BaseComponent> {
     this._initialIsInfinite,
     this._initialIsAlternating, {
     this.isRelative = false,
-    this.curve = Curves.linear,
+    Curve curve,
     this.onComplete,
-  }) {
-    isInfinite = _initialIsInfinite;
-    isAlternating = _initialIsAlternating;
-    curve ??= Curves.linear;
-  }
+  })  : assert(isRelative != null),
+        isInfinite = _initialIsInfinite,
+        isAlternating = _initialIsAlternating,
+        curve = curve ?? Curves.linear;
 
   @mustCallSuper
   void update(double dt) {
@@ -171,12 +170,24 @@ abstract class PositionComponentEffect
   void _setComponentState(Vector2 position, double angle, Vector2 size) {
     if (isRootEffect()) {
       if (modifiesPosition) {
+        assert(
+          position != null,
+          '`position` must not be `null` for an effect which modifies `position`',
+        );
         component?.position?.setFrom(position);
       }
       if (modifiesAngle) {
+        assert(
+          angle != null,
+          '`angle` must not be `null` for an effect which modifies `angle`',
+        );
         component?.angle = angle;
       }
       if (modifiesSize) {
+        assert(
+          size != null,
+          '`size` must not be `null` for an effect which modifies `size`',
+        );
         component?.size?.setFrom(size);
       }
     }
diff --git a/lib/effects/move_effect.dart b/lib/effects/move_effect.dart
index 61aeb26c4..a37138a45 100644
--- a/lib/effects/move_effect.dart
+++ b/lib/effects/move_effect.dart
@@ -50,8 +50,8 @@ class MoveEffect extends SimplePositionComponentEffect {
         );
 
   @override
-  void initialize(_comp) {
-    super.initialize(_comp);
+  void initialize(component) {
+    super.initialize(component);
     List<Vector2> _movePath;
     _startPosition = component.position.clone();
     // With relative here we mean that any vector in the list is relative
@@ -96,7 +96,11 @@ class MoveEffect extends SimplePositionComponentEffect {
     }
     final double totalPathLength = isAlternating ? pathLength * 2 : pathLength;
     speed ??= totalPathLength / duration;
+
+    // `duration` is not null when speed is null
     duration ??= totalPathLength / speed;
+
+    // `speed` is always not null here already
     peakTime = isAlternating ? duration / 2 : duration;
   }
 
diff --git a/lib/effects/rotate_effect.dart b/lib/effects/rotate_effect.dart
index cbc556658..8b6a8f8c6 100644
--- a/lib/effects/rotate_effect.dart
+++ b/lib/effects/rotate_effect.dart
@@ -34,8 +34,8 @@ class RotateEffect extends SimplePositionComponentEffect {
         );
 
   @override
-  void initialize(_comp) {
-    super.initialize(_comp);
+  void initialize(component) {
+    super.initialize(component);
     _startAngle = component.angle;
     _delta = isRelative ? angle : angle - _startAngle;
     if (!isAlternating) {
@@ -49,6 +49,6 @@ class RotateEffect extends SimplePositionComponentEffect {
   @override
   void update(double dt) {
     super.update(dt);
-    component.angle = _startAngle + _delta * curveProgress;
+    component?.angle = _startAngle + _delta * curveProgress;
   }
 }
diff --git a/lib/effects/scale_effect.dart b/lib/effects/scale_effect.dart
index 04a8446fc..ccf5a0f3e 100644
--- a/lib/effects/scale_effect.dart
+++ b/lib/effects/scale_effect.dart
@@ -35,8 +35,8 @@ class ScaleEffect extends SimplePositionComponentEffect {
         );
 
   @override
-  void initialize(_comp) {
-    super.initialize(_comp);
+  void initialize(component) {
+    super.initialize(component);
     _startSize = component.size;
     _delta = isRelative ? size : size - _startSize;
     if (!isAlternating) {
diff --git a/lib/effects/sequence_effect.dart b/lib/effects/sequence_effect.dart
index b885f85fe..432839e86 100644
--- a/lib/effects/sequence_effect.dart
+++ b/lib/effects/sequence_effect.dart
@@ -5,10 +5,14 @@ import 'effects.dart';
 
 class SequenceEffect extends PositionComponentEffect {
   final List<PositionComponentEffect> effects;
-  int _currentIndex;
   PositionComponentEffect currentEffect;
   bool _currentWasAlternating;
-  double _driftModifier;
+
+  static const int _initialIndex = 0;
+  static const double _initialDriftModifier = 0.0;
+
+  int _currentIndex = _initialIndex;
+  double _driftModifier = _initialDriftModifier;
 
   SequenceEffect({
     @required this.effects,
@@ -36,8 +40,8 @@ class SequenceEffect extends PositionComponentEffect {
   @override
   void initialize(PositionComponent component) {
     super.initialize(component);
-    _currentIndex = 0;
-    _driftModifier = 0.0;
+    _currentIndex = _initialIndex;
+    _driftModifier = _initialDriftModifier;
 
     effects.forEach((effect) {
       effect.reset();
diff --git a/lib/flame.dart b/lib/flame.dart
index dd379b807..c1a843f92 100644
--- a/lib/flame.dart
+++ b/lib/flame.dart
@@ -14,8 +14,7 @@ import 'util.dart';
 class Flame {
   // Flame asset bundle, defaults to root
   static AssetBundle _bundle;
-
-  static AssetBundle get bundle => _bundle == null ? rootBundle : _bundle;
+  static AssetBundle get bundle => _bundle ?? rootBundle;
 
   /// Access a shared instance of [AssetsCache] class.
   static AssetsCache assets = AssetsCache();
diff --git a/lib/game/base_game.dart b/lib/game/base_game.dart
index ac8be53d2..4211971d8 100644
--- a/lib/game/base_game.dart
+++ b/lib/game/base_game.dart
@@ -57,9 +57,7 @@ class BaseGame extends Game with FPSCounter {
     }
 
     // first time resize
-    if (size != null) {
-      c.onGameResize(size);
-    }
+    c.onGameResize(size);
   }
 
   /// Prepares and registers a component to be added on the next game tick
diff --git a/lib/game/game_widget.dart b/lib/game/game_widget.dart
index b76e3606a..6e157e8f5 100644
--- a/lib/game/game_widget.dart
+++ b/lib/game/game_widget.dart
@@ -134,12 +134,13 @@ class _GameWidgetState<T extends Game> extends State<GameWidget<T>> {
   }
 
   void _initActiveOverlays() {
-    if (widget.initialActiveOverlays != null) {
-      _checkOverlays(widget.initialActiveOverlays.toSet());
-      widget.initialActiveOverlays.forEach((key) {
-        widget.game.overlays.add(key);
-      });
+    if (widget.initialActiveOverlays == null) {
+      return;
     }
+    _checkOverlays(widget.initialActiveOverlays.toSet());
+    widget.initialActiveOverlays.forEach((key) {
+      widget.game.overlays.add(key);
+    });
   }
 
   @override
@@ -175,8 +176,10 @@ class _GameWidgetState<T extends Game> extends State<GameWidget<T>> {
 
   void _checkOverlays(Set<String> overlays) {
     overlays.forEach((overlayKey) {
-      assert(widget.overlayBuilderMap.containsKey(overlayKey),
-          "A non mapped overlay has been added: $overlayKey");
+      assert(
+        widget.overlayBuilderMap?.containsKey(overlayKey) ?? false,
+        "A non mapped overlay has been added: $overlayKey",
+      );
     });
   }
 
@@ -472,10 +475,9 @@ Widget _applyAdvancedGesturesDetectors(Game game, Widget child) {
       (MultiDragGestureRecognizer instance) {
         instance
           ..onStart = (Offset o) {
-            final drag = DragEvent();
             // Note that padding or margin isn't taken into account here
-            drag.initialPosition = o;
-            dragHandlers.forEach((h) => h.onReceiveDrag(drag));
+            final drag = DragEvent(o);
+            dragHandlers.forEach((h) => h.onReceiveDrag?.call(drag));
             return drag;
           };
       },
diff --git a/lib/gestures.dart b/lib/gestures.dart
index a15d57bb6..252d51668 100644
--- a/lib/gestures.dart
+++ b/lib/gestures.dart
@@ -11,7 +11,9 @@ mixin MultiTouchTapDetector on Game {
 }
 
 class DragEvent extends Drag {
-  Offset initialPosition;
+  final Offset initialPosition;
+
+  DragEvent(this.initialPosition);
 
   void Function(DragUpdateDetails) onUpdate;
   void Function() onCancel;
diff --git a/lib/layers/processors.dart b/lib/layers/processors.dart
index fc52a2cf9..7e21f97a4 100644
--- a/lib/layers/processors.dart
+++ b/lib/layers/processors.dart
@@ -5,7 +5,7 @@ abstract class LayerProcessor {
 }
 
 class ShadowProcessor extends LayerProcessor {
-  Paint _shadowPaint;
+  final Paint _shadowPaint;
 
   final Offset offset;
 
@@ -13,11 +13,9 @@ class ShadowProcessor extends LayerProcessor {
     this.offset = const Offset(10, 10),
     double opacity = 0.9,
     Color color = const Color(0xFF000000),
-  }) {
-    _shadowPaint = Paint()
-      ..colorFilter =
-          ColorFilter.mode(color.withOpacity(opacity), BlendMode.srcATop);
-  }
+  }) : _shadowPaint = Paint()
+          ..colorFilter =
+              ColorFilter.mode(color.withOpacity(opacity), BlendMode.srcATop);
 
   @override
   void process(Picture pic, Canvas canvas) {
diff --git a/lib/nine_tile_box.dart b/lib/nine_tile_box.dart
index 9b918dd00..6c6fbb034 100644
--- a/lib/nine_tile_box.dart
+++ b/lib/nine_tile_box.dart
@@ -30,9 +30,9 @@ class NineTileBox {
   ///
   /// If [destTileSize] is not provided, the evaluated [tileSize] is used instead
   /// (so no scaling happens).
-  NineTileBox(this.sprite, {int tileSize, int destTileSize}) {
-    this.tileSize = tileSize ?? sprite.src.width.toInt();
-    this.destTileSize = destTileSize ?? tileSize;
+  NineTileBox(this.sprite, {int tileSize, int destTileSize})
+      : tileSize = tileSize ?? sprite.src.width.toInt() {
+    this.destTileSize = destTileSize ?? this.tileSize;
   }
 
   /// Renders this nine box with the dimensions provided by [rect].
diff --git a/lib/parallax.dart b/lib/parallax.dart
index 8f943034b..274c1aeeb 100644
--- a/lib/parallax.dart
+++ b/lib/parallax.dart
@@ -121,10 +121,8 @@ class ParallaxLayer {
   /// multiplying the [baseVelocity] with the [velocityMultiplier].
   ParallaxLayer(
     this.parallaxImage, {
-    this.velocityMultiplier,
-  }) {
-    velocityMultiplier ??= Vector2.all(1.0);
-  }
+    Vector2 velocityMultiplier,
+  }) : velocityMultiplier = velocityMultiplier ?? Vector2.all(1.0);
 
   Vector2 currentOffset() => _scroll;
 
@@ -241,10 +239,8 @@ class Parallax {
 
   Parallax(
     this.layers, {
-    this.baseVelocity,
-  }) {
-    baseVelocity ??= Vector2.zero();
-  }
+    Vector2 baseVelocity,
+  }) : baseVelocity = baseVelocity ?? Vector2.zero();
 
   /// The base offset of the parallax, can be used in an outer update loop
   /// if you want to transition the parallax to a certain position.
diff --git a/lib/particles/computed_particle.dart b/lib/particles/computed_particle.dart
index 4d8b8b9d4..0ee9216dd 100644
--- a/lib/particles/computed_particle.dart
+++ b/lib/particles/computed_particle.dart
@@ -19,7 +19,6 @@ class ComputedParticle extends Particle {
   ComputedParticle({
     @required this.renderer,
     double lifespan,
-    Duration duration,
   }) : super(
           lifespan: lifespan,
         );
diff --git a/lib/particles/rotating_particle.dart b/lib/particles/rotating_particle.dart
index f8e92026d..eca8136fb 100644
--- a/lib/particles/rotating_particle.dart
+++ b/lib/particles/rotating_particle.dart
@@ -25,7 +25,7 @@ class RotatingParticle extends CurvedParticle with SingleChildParticle {
           lifespan: lifespan,
         );
 
-  double get angle => lerpDouble(from, to, progress);
+  double get angle => lerpDouble(from, to, progress) ?? 0;
 
   @override
   void render(Canvas canvas) {
diff --git a/lib/sprite.dart b/lib/sprite.dart
index cdb213465..d757c853f 100644
--- a/lib/sprite.dart
+++ b/lib/sprite.dart
@@ -10,7 +10,7 @@ import 'assets/images.dart';
 class Sprite {
   Paint paint = BasicPalette.white.paint;
   Image image;
-  Rect src;
+  Rect src = Rect.zero;
 
   Sprite(
     this.image, {
@@ -44,10 +44,10 @@ class Sprite {
 
   set srcSize(Vector2 size) {
     size ??= Vector2Extension.fromInts(image.width, image.height);
-    src = (srcPosition ?? Vector2.zero()).toPositionedRect(size);
+    src = srcPosition.toPositionedRect(size);
   }
 
-  Vector2 get srcPosition => (src?.topLeft ?? Offset.zero).toVector2();
+  Vector2 get srcPosition => src.topLeft.toVector2();
 
   set srcPosition(Vector2 position) {
     src = (position ?? Vector2.zero()).toPositionedRect(srcSize);
diff --git a/lib/widgets/animation_widget.dart b/lib/widgets/animation_widget.dart
index 155aade40..b8744e0e0 100644
--- a/lib/widgets/animation_widget.dart
+++ b/lib/widgets/animation_widget.dart
@@ -50,7 +50,7 @@ class _AnimationWidget extends State<SpriteAnimationWidget>
       ..addListener(() {
         final now = DateTime.now().millisecond.toDouble();
 
-        final dt = max(0, (now - _lastUpdated) / 1000).toDouble();
+        final dt = max(0, (now - (_lastUpdated ?? 0)) / 1000).toDouble();
         widget.animation.update(dt);
 
         setState(() {