diff --git a/CHANGELOG.md b/CHANGELOG.md
index 054bf2f..b50159b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+## 0.6.0
+### Changed
+* Migrated to sound null-safety.
+* Increase the minimum version of Flutter.
+* Increase the minimum version of Dart SDK.
+
 ## 0.5.0
 ### Changed
 * The minimum version of Flutter.
diff --git a/example/lib/common.dart b/example/lib/common.dart
index 046d93e..b66a549 100644
--- a/example/lib/common.dart
+++ b/example/lib/common.dart
@@ -3,9 +3,9 @@ import 'package:flutter_sticky_header/flutter_sticky_header.dart';
 
 class AppScaffold extends StatelessWidget {
   const AppScaffold({
-    Key key,
-    @required this.title,
-    @required this.slivers,
+    Key? key,
+    required this.title,
+    required this.slivers,
     this.reverse = false,
   }) : super(key: key);
 
@@ -32,7 +32,7 @@ class AppScaffold extends StatelessWidget {
 
 class _FloatingActionButton extends StatelessWidget {
   const _FloatingActionButton({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -42,8 +42,8 @@ class _FloatingActionButton extends StatelessWidget {
       backgroundColor: Colors.green,
       onPressed: () {
         final double offset =
-            DefaultStickyHeaderController.of(context).stickyHeaderScrollOffset;
-        PrimaryScrollController.of(context).animateTo(
+            DefaultStickyHeaderController.of(context)!.stickyHeaderScrollOffset;
+        PrimaryScrollController.of(context)!.animateTo(
           offset,
           duration: Duration(milliseconds: 300),
           curve: Curves.easeIn,
@@ -55,14 +55,14 @@ class _FloatingActionButton extends StatelessWidget {
 
 class Header extends StatelessWidget {
   const Header({
-    Key key,
+    Key? key,
     this.index,
     this.title,
     this.color = Colors.lightBlue,
   }) : super(key: key);
 
-  final String title;
-  final int index;
+  final String? title;
+  final int? index;
   final Color color;
 
   @override
diff --git a/example/lib/examples/animated_header.dart b/example/lib/examples/animated_header.dart
index 01237e8..f624c57 100644
--- a/example/lib/examples/animated_header.dart
+++ b/example/lib/examples/animated_header.dart
@@ -5,7 +5,7 @@ import '../common.dart';
 
 class AnimatedHeaderExample extends StatelessWidget {
   const AnimatedHeaderExample({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -24,11 +24,11 @@ class AnimatedHeaderExample extends StatelessWidget {
 
 class _StickyHeaderList extends StatelessWidget {
   const _StickyHeaderList({
-    Key key,
+    Key? key,
     this.index,
   }) : super(key: key);
 
-  final int index;
+  final int? index;
 
   @override
   Widget build(BuildContext context) {
@@ -54,19 +54,19 @@ class _StickyHeaderList extends StatelessWidget {
 
 class _AnimatedHeader extends StatelessWidget {
   const _AnimatedHeader({
-    Key key,
+    Key? key,
     this.state,
     this.index,
   }) : super(key: key);
 
-  final int index;
-  final SliverStickyHeaderState state;
+  final int? index;
+  final SliverStickyHeaderState? state;
 
   @override
   Widget build(BuildContext context) {
     return Header(
       index: index,
-      color: Colors.lightBlue.withOpacity(1 - state.scrollPercentage),
+      color: Colors.lightBlue.withOpacity(1 - state!.scrollPercentage),
     );
   }
 }
diff --git a/example/lib/examples/grid.dart b/example/lib/examples/grid.dart
index 2b2312f..da1af75 100644
--- a/example/lib/examples/grid.dart
+++ b/example/lib/examples/grid.dart
@@ -5,7 +5,7 @@ import '../common.dart';
 
 class GridExample extends StatelessWidget {
   const GridExample({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -24,11 +24,11 @@ class GridExample extends StatelessWidget {
 
 class _StickyHeaderGrid extends StatelessWidget {
   const _StickyHeaderGrid({
-    Key key,
+    Key? key,
     this.index,
   }) : super(key: key);
 
-  final int index;
+  final int? index;
 
   @override
   Widget build(BuildContext context) {
diff --git a/example/lib/examples/list.dart b/example/lib/examples/list.dart
index f94f841..27f5c42 100644
--- a/example/lib/examples/list.dart
+++ b/example/lib/examples/list.dart
@@ -5,7 +5,7 @@ import '../common.dart';
 
 class ListExample extends StatelessWidget {
   const ListExample({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -24,11 +24,11 @@ class ListExample extends StatelessWidget {
 
 class _StickyHeaderList extends StatelessWidget {
   const _StickyHeaderList({
-    Key key,
+    Key? key,
     this.index,
   }) : super(key: key);
 
-  final int index;
+  final int? index;
 
   @override
   Widget build(BuildContext context) {
diff --git a/example/lib/examples/mix_slivers.dart b/example/lib/examples/mix_slivers.dart
index 698c352..ce4b8e3 100644
--- a/example/lib/examples/mix_slivers.dart
+++ b/example/lib/examples/mix_slivers.dart
@@ -5,7 +5,7 @@ import '../common.dart';
 
 class MixSliversExample extends StatelessWidget {
   const MixSliversExample({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -36,11 +36,11 @@ class MixSliversExample extends StatelessWidget {
 
 class _StickyHeaderList extends StatelessWidget {
   const _StickyHeaderList({
-    Key key,
+    Key? key,
     this.index,
   }) : super(key: key);
 
-  final int index;
+  final int? index;
 
   @override
   Widget build(BuildContext context) {
diff --git a/example/lib/examples/not_sticky.dart b/example/lib/examples/not_sticky.dart
index af205f2..a6d7015 100644
--- a/example/lib/examples/not_sticky.dart
+++ b/example/lib/examples/not_sticky.dart
@@ -5,7 +5,7 @@ import '../common.dart';
 
 class NotStickyExample extends StatelessWidget {
   const NotStickyExample({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -24,11 +24,11 @@ class NotStickyExample extends StatelessWidget {
 
 class _NotStickyList extends StatelessWidget {
   const _NotStickyList({
-    Key key,
+    Key? key,
     this.index,
   }) : super(key: key);
 
-  final int index;
+  final int? index;
 
   @override
   Widget build(BuildContext context) {
diff --git a/example/lib/examples/reverse.dart b/example/lib/examples/reverse.dart
index 9279f76..17fea56 100644
--- a/example/lib/examples/reverse.dart
+++ b/example/lib/examples/reverse.dart
@@ -5,7 +5,7 @@ import '../common.dart';
 
 class ReverseExample extends StatelessWidget {
   const ReverseExample({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -25,11 +25,11 @@ class ReverseExample extends StatelessWidget {
 
 class _StickyHeaderList extends StatelessWidget {
   const _StickyHeaderList({
-    Key key,
+    Key? key,
     this.index,
   }) : super(key: key);
 
-  final int index;
+  final int? index;
 
   @override
   Widget build(BuildContext context) {
diff --git a/example/lib/examples/side_header.dart b/example/lib/examples/side_header.dart
index 8c6074e..a7602da 100644
--- a/example/lib/examples/side_header.dart
+++ b/example/lib/examples/side_header.dart
@@ -5,7 +5,7 @@ import '../common.dart';
 
 class SideHeaderExample extends StatelessWidget {
   const SideHeaderExample({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -24,11 +24,11 @@ class SideHeaderExample extends StatelessWidget {
 
 class _StickyHeaderGrid extends StatelessWidget {
   const _StickyHeaderGrid({
-    Key key,
+    Key? key,
     this.index,
   }) : super(key: key);
 
-  final int index;
+  final int? index;
 
   @override
   Widget build(BuildContext context) {
@@ -68,11 +68,11 @@ class _StickyHeaderGrid extends StatelessWidget {
 
 class _SideHeader extends StatelessWidget {
   const _SideHeader({
-    Key key,
+    Key? key,
     this.index,
   }) : super(key: key);
 
-  final int index;
+  final int? index;
 
   @override
   Widget build(BuildContext context) {
diff --git a/example/lib/main.dart b/example/lib/main.dart
index a2cdd50..e1ddcc5 100644
--- a/example/lib/main.dart
+++ b/example/lib/main.dart
@@ -1,18 +1,18 @@
 import 'package:flutter/material.dart';
 
-import 'examples/list.dart';
+import 'examples/animated_header.dart';
 import 'examples/grid.dart';
+import 'examples/list.dart';
+import 'examples/mix_slivers.dart';
 import 'examples/not_sticky.dart';
-import 'examples/side_header.dart';
-import 'examples/animated_header.dart';
 import 'examples/reverse.dart';
-import 'examples/mix_slivers.dart';
+import 'examples/side_header.dart';
 
 void main() => runApp(const App());
 
 class App extends StatelessWidget {
   const App({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -26,7 +26,7 @@ class App extends StatelessWidget {
 
 class _Home extends StatelessWidget {
   const _Home({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -73,9 +73,9 @@ class _Home extends StatelessWidget {
 
 class _Item extends StatelessWidget {
   const _Item({
-    Key key,
-    @required this.text,
-    @required this.builder,
+    Key? key,
+    required this.text,
+    required this.builder,
   }) : super(key: key);
 
   final String text;
diff --git a/example/pubspec.yaml b/example/pubspec.yaml
index 04c5dc2..08a01a8 100644
--- a/example/pubspec.yaml
+++ b/example/pubspec.yaml
@@ -18,7 +18,7 @@ publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 version: 1.0.0+1
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: '>=2.12.0 <3.0.0'
 
 dependencies:
   flutter:
@@ -29,7 +29,7 @@ dependencies:
 
   # The following adds the Cupertino Icons font to your application.
   # Use with the CupertinoIcons class for iOS style icons.
-  cupertino_icons: ^0.1.3
+  cupertino_icons: ^1.0.2
 
 dev_dependencies:
   flutter_test:
diff --git a/lib/src/rendering/sliver_sticky_header.dart b/lib/src/rendering/sliver_sticky_header.dart
index 83b7262..a1c300a 100644
--- a/lib/src/rendering/sliver_sticky_header.dart
+++ b/lib/src/rendering/sliver_sticky_header.dart
@@ -12,28 +12,26 @@ import 'package:value_layout_builder/value_layout_builder.dart';
 /// the [child] scrolls off the viewport.
 class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
   RenderSliverStickyHeader({
-    RenderObject header,
-    RenderSliver child,
+    RenderObject? header,
+    RenderSliver? child,
     bool overlapsContent: false,
     bool sticky: true,
-    StickyHeaderController controller,
-  })  : assert(overlapsContent != null),
-        assert(sticky != null),
-        _overlapsContent = overlapsContent,
+    StickyHeaderController? controller,
+  })  : _overlapsContent = overlapsContent,
         _sticky = sticky,
         _controller = controller {
-    this.header = header;
+    this.header = header as RenderBox?;
     this.child = child;
   }
 
-  SliverStickyHeaderState _oldState;
-  double _headerExtent;
-  bool _isPinned;
+  SliverStickyHeaderState? _oldState;
+  double? _headerExtent;
+  late bool _isPinned;
 
   bool get overlapsContent => _overlapsContent;
   bool _overlapsContent;
+
   set overlapsContent(bool value) {
-    assert(value != null);
     if (_overlapsContent == value) return;
     _overlapsContent = value;
     markNeedsLayout();
@@ -41,40 +39,43 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
 
   bool get sticky => _sticky;
   bool _sticky;
+
   set sticky(bool value) {
-    assert(value != null);
     if (_sticky == value) return;
     _sticky = value;
     markNeedsLayout();
   }
 
-  StickyHeaderController get controller => _controller;
-  StickyHeaderController _controller;
-  set controller(StickyHeaderController value) {
+  StickyHeaderController? get controller => _controller;
+  StickyHeaderController? _controller;
+
+  set controller(StickyHeaderController? value) {
     if (_controller == value) return;
     if (_controller != null && value != null) {
       // We copy the state of the old controller.
-      value.stickyHeaderScrollOffset = _controller.stickyHeaderScrollOffset;
+      value.stickyHeaderScrollOffset = _controller!.stickyHeaderScrollOffset;
     }
     _controller = value;
   }
 
   /// The render object's header
-  RenderBox get header => _header;
-  RenderBox _header;
-  set header(RenderBox value) {
-    if (_header != null) dropChild(_header);
+  RenderBox? get header => _header;
+  RenderBox? _header;
+
+  set header(RenderBox? value) {
+    if (_header != null) dropChild(_header!);
     _header = value;
-    if (_header != null) adoptChild(_header);
+    if (_header != null) adoptChild(_header!);
   }
 
   /// The render object's unique child
-  RenderSliver get child => _child;
-  RenderSliver _child;
-  set child(RenderSliver value) {
-    if (_child != null) dropChild(_child);
+  RenderSliver? get child => _child;
+  RenderSliver? _child;
+
+  set child(RenderSliver? value) {
+    if (_child != null) dropChild(_child!);
     _child = value;
-    if (_child != null) adoptChild(_child);
+    if (_child != null) adoptChild(_child!);
   }
 
   @override
@@ -86,55 +87,53 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
   @override
   void attach(PipelineOwner owner) {
     super.attach(owner);
-    if (_header != null) _header.attach(owner);
-    if (_child != null) _child.attach(owner);
+    if (_header != null) _header!.attach(owner);
+    if (_child != null) _child!.attach(owner);
   }
 
   @override
   void detach() {
     super.detach();
-    if (_header != null) _header.detach();
-    if (_child != null) _child.detach();
+    if (_header != null) _header!.detach();
+    if (_child != null) _child!.detach();
   }
 
   @override
   void redepthChildren() {
-    if (_header != null) redepthChild(_header);
-    if (_child != null) redepthChild(_child);
+    if (_header != null) redepthChild(_header!);
+    if (_child != null) redepthChild(_child!);
   }
 
   @override
   void visitChildren(RenderObjectVisitor visitor) {
-    if (_header != null) visitor(_header);
-    if (_child != null) visitor(_child);
+    if (_header != null) visitor(_header!);
+    if (_child != null) visitor(_child!);
   }
 
   @override
   List<DiagnosticsNode> debugDescribeChildren() {
     List<DiagnosticsNode> result = <DiagnosticsNode>[];
     if (header != null) {
-      result.add(header.toDiagnosticsNode(name: 'header'));
+      result.add(header!.toDiagnosticsNode(name: 'header'));
     }
     if (child != null) {
-      result.add(child.toDiagnosticsNode(name: 'child'));
+      result.add(child!.toDiagnosticsNode(name: 'child'));
     }
     return result;
   }
 
   double computeHeaderExtent() {
     if (header == null) return 0.0;
-    assert(header.hasSize);
-    assert(constraints.axis != null);
+    assert(header!.hasSize);
     switch (constraints.axis) {
       case Axis.vertical:
-        return header.size.height;
+        return header!.size.height;
       case Axis.horizontal:
-        return header.size.width;
+        return header!.size.width;
     }
-    return null;
   }
 
-  double get headerLogicalExtent => overlapsContent ? 0.0 : _headerExtent;
+  double? get headerLogicalExtent => overlapsContent ? 0.0 : _headerExtent;
 
   @override
   void performLayout() {
@@ -148,7 +147,7 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
         constraints.axisDirection, constraints.growthDirection);
 
     if (header != null) {
-      header.layout(
+      header!.layout(
         BoxValueConstraints<SliverStickyHeaderState>(
           value: _oldState ?? SliverStickyHeaderState(0.0, false),
           constraints: constraints.asBoxConstraints(),
@@ -159,7 +158,7 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
     }
 
     // Compute the header extent only one time.
-    double headerExtent = headerLogicalExtent;
+    double headerExtent = headerLogicalExtent!;
     final double headerPaintExtent =
         calculatePaintOffset(constraints, from: 0.0, to: headerExtent);
     final double headerCacheExtent =
@@ -175,7 +174,7 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
           hasVisualOverflow: headerExtent > constraints.remainingPaintExtent ||
               constraints.scrollOffset > 0.0);
     } else {
-      child.layout(
+      child!.layout(
         constraints.copyWith(
           scrollOffset: math.max(0.0, constraints.scrollOffset - headerExtent),
           cacheOrigin: math.min(0.0, constraints.cacheOrigin + headerExtent),
@@ -187,7 +186,7 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
         ),
         parentUsesSize: true,
       );
-      final SliverGeometry childLayoutGeometry = child.geometry;
+      final SliverGeometry childLayoutGeometry = child!.geometry!;
       if (childLayoutGeometry.scrollOffsetCorrection != null) {
         geometry = SliverGeometry(
           scrollOffsetCorrection: childLayoutGeometry.scrollOffsetCorrection,
@@ -217,37 +216,37 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
         hasVisualOverflow: childLayoutGeometry.hasVisualOverflow,
       );
 
-      final SliverPhysicalParentData childParentData = child.parentData;
-      assert(constraints.axisDirection != null);
-      assert(constraints.growthDirection != null);
+      final SliverPhysicalParentData? childParentData =
+          child!.parentData as SliverPhysicalParentData?;
       switch (axisDirection) {
         case AxisDirection.up:
-          childParentData.paintOffset = Offset.zero;
+          childParentData!.paintOffset = Offset.zero;
           break;
         case AxisDirection.right:
-          childParentData.paintOffset = Offset(
+          childParentData!.paintOffset = Offset(
               calculatePaintOffset(constraints, from: 0.0, to: headerExtent),
               0.0);
           break;
         case AxisDirection.down:
-          childParentData.paintOffset = Offset(0.0,
+          childParentData!.paintOffset = Offset(0.0,
               calculatePaintOffset(constraints, from: 0.0, to: headerExtent));
           break;
         case AxisDirection.left:
-          childParentData.paintOffset = Offset.zero;
+          childParentData!.paintOffset = Offset.zero;
           break;
       }
     }
 
     if (header != null) {
-      final SliverPhysicalParentData headerParentData = header.parentData;
+      final SliverPhysicalParentData? headerParentData =
+          header!.parentData as SliverPhysicalParentData?;
       final double childScrollExtent = child?.geometry?.scrollExtent ?? 0.0;
       final double headerPosition = sticky
           ? math.min(
               constraints.overlap,
               childScrollExtent -
                   constraints.scrollOffset -
-                  (overlapsContent ? _headerExtent : 0.0))
+                  (overlapsContent ? _headerExtent! : 0.0))
           : -constraints.scrollOffset;
 
       _isPinned = sticky &&
@@ -256,7 +255,7 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
                   constraints.viewportMainAxisExtent);
 
       final double headerScrollRatio =
-          ((headerPosition - constraints.overlap).abs() / _headerExtent);
+          ((headerPosition - constraints.overlap).abs() / _headerExtent!);
       if (_isPinned && headerScrollRatio <= 1) {
         controller?.stickyHeaderScrollOffset =
             constraints.precedingScrollExtent;
@@ -271,8 +270,8 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
             SliverStickyHeaderState(headerScrollRatioClamped, _isPinned);
         if (_oldState != state) {
           _oldState = state;
-          header.layout(
-            BoxValueConstraints<SliverStickyHeaderState>(
+          header!.layout(
+            BoxValueConstraints<SliverStickyHeaderState?>(
               value: _oldState,
               constraints: constraints.asBoxConstraints(),
             ),
@@ -283,18 +282,18 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
 
       switch (axisDirection) {
         case AxisDirection.up:
-          headerParentData.paintOffset = Offset(
-              0.0, geometry.paintExtent - headerPosition - _headerExtent);
+          headerParentData!.paintOffset = Offset(
+              0.0, geometry!.paintExtent - headerPosition - _headerExtent!);
           break;
         case AxisDirection.down:
-          headerParentData.paintOffset = Offset(0.0, headerPosition);
+          headerParentData!.paintOffset = Offset(0.0, headerPosition);
           break;
         case AxisDirection.left:
-          headerParentData.paintOffset = Offset(
-              geometry.paintExtent - headerPosition - _headerExtent, 0.0);
+          headerParentData!.paintOffset = Offset(
+              geometry!.paintExtent - headerPosition - _headerExtent!, 0.0);
           break;
         case AxisDirection.right:
-          headerParentData.paintOffset = Offset(headerPosition, 0.0);
+          headerParentData!.paintOffset = Offset(headerPosition, 0.0);
           break;
       }
     }
@@ -302,25 +301,25 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
 
   @override
   bool hitTestChildren(SliverHitTestResult result,
-      {@required double mainAxisPosition, @required double crossAxisPosition}) {
-    assert(geometry.hitTestExtent > 0.0);
+      {required double mainAxisPosition, required double crossAxisPosition}) {
+    assert(geometry!.hitTestExtent > 0.0);
     if (header != null &&
-        mainAxisPosition - constraints.overlap <= _headerExtent) {
+        mainAxisPosition - constraints.overlap <= _headerExtent!) {
       return hitTestBoxChild(
             BoxHitTestResult.wrap(SliverHitTestResult.wrap(result)),
-            header,
+            header!,
             mainAxisPosition: mainAxisPosition - constraints.overlap,
             crossAxisPosition: crossAxisPosition,
           ) ||
           (_overlapsContent &&
               child != null &&
-              child.geometry.hitTestExtent > 0.0 &&
-              child.hitTest(result,
+              child!.geometry!.hitTestExtent > 0.0 &&
+              child!.hitTest(result,
                   mainAxisPosition:
                       mainAxisPosition - childMainAxisPosition(child),
                   crossAxisPosition: crossAxisPosition));
-    } else if (child != null && child.geometry.hitTestExtent > 0.0) {
-      return child.hitTest(result,
+    } else if (child != null && child!.geometry!.hitTestExtent > 0.0) {
+      return child!.hitTest(result,
           mainAxisPosition: mainAxisPosition - childMainAxisPosition(child),
           crossAxisPosition: crossAxisPosition);
     }
@@ -328,19 +327,19 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
   }
 
   @override
-  double childMainAxisPosition(RenderObject child) {
+  double childMainAxisPosition(RenderObject? child) {
     if (child == header)
       return _isPinned
           ? 0.0
           : -(constraints.scrollOffset + constraints.overlap);
     if (child == this.child)
       return calculatePaintOffset(constraints,
-          from: 0.0, to: headerLogicalExtent);
-    return null;
+          from: 0.0, to: headerLogicalExtent!);
+    return 0;
   }
 
   @override
-  double childScrollOffset(RenderObject child) {
+  double? childScrollOffset(RenderObject child) {
     assert(child.parent == this);
     if (child == this.child) {
       return _headerExtent;
@@ -351,23 +350,25 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
 
   @override
   void applyPaintTransform(RenderObject child, Matrix4 transform) {
-    assert(child != null);
-    final SliverPhysicalParentData childParentData = child.parentData;
+    final SliverPhysicalParentData childParentData =
+        child.parentData as SliverPhysicalParentData;
     childParentData.applyPaintTransform(transform);
   }
 
   @override
   void paint(PaintingContext context, Offset offset) {
-    if (geometry.visible) {
-      if (child != null && child.geometry.visible) {
-        final SliverPhysicalParentData childParentData = child.parentData;
-        context.paintChild(child, offset + childParentData.paintOffset);
+    if (geometry!.visible) {
+      if (child != null && child!.geometry!.visible) {
+        final SliverPhysicalParentData childParentData =
+            child!.parentData as SliverPhysicalParentData;
+        context.paintChild(child!, offset + childParentData.paintOffset);
       }
 
       // The header must be drawn over the sliver.
       if (header != null) {
-        final SliverPhysicalParentData headerParentData = header.parentData;
-        context.paintChild(header, offset + headerParentData.paintOffset);
+        final SliverPhysicalParentData headerParentData =
+            header!.parentData as SliverPhysicalParentData;
+        context.paintChild(header!, offset + headerParentData.paintOffset);
       }
     }
   }
diff --git a/lib/src/widgets/sliver_sticky_header.dart b/lib/src/widgets/sliver_sticky_header.dart
index df2e05c..48d0657 100644
--- a/lib/src/widgets/sliver_sticky_header.dart
+++ b/lib/src/widgets/sliver_sticky_header.dart
@@ -1,3 +1,4 @@
+import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_sticky_header/src/rendering/sliver_sticky_header.dart';
 import 'package:value_layout_builder/value_layout_builder.dart';
@@ -20,7 +21,6 @@ class StickyHeaderController with ChangeNotifier {
 
   /// This setter should only be used by flutter_sticky_header package.
   set stickyHeaderScrollOffset(double value) {
-    assert(value != null);
     if (_stickyHeaderScrollOffset != value) {
       _stickyHeaderScrollOffset = value;
       notifyListeners();
@@ -38,8 +38,8 @@ class StickyHeaderController with ChangeNotifier {
 /// widgets.
 class DefaultStickyHeaderController extends StatefulWidget {
   const DefaultStickyHeaderController({
-    Key key,
-    @required this.child,
+    Key? key,
+    required this.child,
   }) : super(key: key);
 
   /// The widget below this widget in the tree.
@@ -56,8 +56,8 @@ class DefaultStickyHeaderController extends StatefulWidget {
   /// ```dart
   /// StickyHeaderController controller = DefaultStickyHeaderController.of(context);
   /// ```
-  static StickyHeaderController of(BuildContext context) {
-    final _StickyHeaderControllerScope scope = context
+  static StickyHeaderController? of(BuildContext context) {
+    final _StickyHeaderControllerScope? scope = context
         .dependOnInheritedWidgetOfExactType<_StickyHeaderControllerScope>();
     return scope?.controller;
   }
@@ -69,7 +69,7 @@ class DefaultStickyHeaderController extends StatefulWidget {
 
 class _DefaultStickyHeaderControllerState
     extends State<DefaultStickyHeaderController> {
-  StickyHeaderController _controller;
+  StickyHeaderController? _controller;
 
   @override
   void initState() {
@@ -79,7 +79,7 @@ class _DefaultStickyHeaderControllerState
 
   @override
   void dispose() {
-    _controller.dispose();
+    _controller!.dispose();
     super.dispose();
   }
 
@@ -94,12 +94,12 @@ class _DefaultStickyHeaderControllerState
 
 class _StickyHeaderControllerScope extends InheritedWidget {
   const _StickyHeaderControllerScope({
-    Key key,
+    Key? key,
     this.controller,
-    Widget child,
+    required Widget child,
   }) : super(key: key, child: child);
 
-  final StickyHeaderController controller;
+  final StickyHeaderController? controller;
 
   @override
   bool updateShouldNotify(_StickyHeaderControllerScope old) {
@@ -113,8 +113,7 @@ class SliverStickyHeaderState {
   const SliverStickyHeaderState(
     this.scrollPercentage,
     this.isPinned,
-  )   : assert(scrollPercentage != null),
-        assert(isPinned != null);
+  );
 
   final double scrollPercentage;
 
@@ -150,15 +149,13 @@ class SliverStickyHeader extends RenderObjectWidget {
   /// If a [StickyHeaderController] is not provided, then the value of
   /// [DefaultStickyHeaderController.of] will be used.
   SliverStickyHeader({
-    Key key,
+    Key? key,
     this.header,
     this.sliver,
     this.overlapsContent: false,
     this.sticky = true,
     this.controller,
-  })  : assert(overlapsContent != null),
-        assert(sticky != null),
-        super(key: key);
+  }) : super(key: key);
 
   /// Creates a widget that builds the header of a [SliverStickyHeader]
   /// each time its scroll percentage changes.
@@ -168,12 +165,12 @@ class SliverStickyHeader extends RenderObjectWidget {
   /// If a [StickyHeaderController] is not provided, then the value of
   /// [DefaultStickyHeaderController.of] will be used.
   SliverStickyHeader.builder({
-    Key key,
-    SliverStickyHeaderWidgetBuilder builder,
-    Widget sliver,
+    Key? key,
+    required SliverStickyHeaderWidgetBuilder builder,
+    Widget? sliver,
     bool overlapsContent: false,
     bool sticky = true,
-    StickyHeaderController controller,
+    StickyHeaderController? controller,
   }) : this(
           key: key,
           header: ValueLayoutBuilder<SliverStickyHeaderState>(
@@ -187,10 +184,10 @@ class SliverStickyHeader extends RenderObjectWidget {
         );
 
   /// The header to display before the sliver.
-  final Widget header;
+  final Widget? header;
 
   /// The sliver to display after the header.
-  final Widget sliver;
+  final Widget? sliver;
 
   /// Whether the header should be drawn on top of the sliver
   /// instead of before.
@@ -204,7 +201,7 @@ class SliverStickyHeader extends RenderObjectWidget {
   ///
   /// If a [StickyHeaderController] is not provided, then the value of [DefaultStickyHeaderController.of]
   /// will be used.
-  final StickyHeaderController controller;
+  final StickyHeaderController? controller;
 
   @override
   RenderSliverStickyHeader createRenderObject(BuildContext context) {
@@ -247,16 +244,13 @@ class SliverStickyHeaderBuilder extends StatelessWidget {
   /// If a [StickyHeaderController] is not provided, then the value of [DefaultStickyHeaderController.of]
   /// will be used.
   const SliverStickyHeaderBuilder({
-    Key key,
-    @required this.builder,
+    Key? key,
+    required this.builder,
     this.sliver,
     this.overlapsContent: false,
     this.sticky = true,
     this.controller,
-  })  : assert(builder != null),
-        assert(overlapsContent != null),
-        assert(sticky != null),
-        super(key: key);
+  }) : super(key: key);
 
   /// Called to build the [SliverStickyHeader]'s header.
   ///
@@ -265,7 +259,7 @@ class SliverStickyHeaderBuilder extends StatelessWidget {
   final SliverStickyHeaderWidgetBuilder builder;
 
   /// The sliver to display after the header.
-  final Widget sliver;
+  final Widget? sliver;
 
   /// Whether the header should be drawn on top of the sliver
   /// instead of before.
@@ -279,7 +273,7 @@ class SliverStickyHeaderBuilder extends StatelessWidget {
   ///
   /// If a [StickyHeaderController] is not provided, then the value of [DefaultStickyHeaderController.of]
   /// will be used.
-  final StickyHeaderController controller;
+  final StickyHeaderController? controller;
 
   @override
   Widget build(BuildContext context) {
@@ -301,16 +295,16 @@ class SliverStickyHeaderRenderObjectElement extends RenderObjectElement {
       : super(widget);
 
   @override
-  SliverStickyHeader get widget => super.widget;
+  SliverStickyHeader get widget => super.widget as SliverStickyHeader;
 
-  Element _header;
+  Element? _header;
 
-  Element _sliver;
+  Element? _sliver;
 
   @override
   void visitChildren(ElementVisitor visitor) {
-    if (_header != null) visitor(_header);
-    if (_sliver != null) visitor(_sliver);
+    if (_header != null) visitor(_header!);
+    if (_sliver != null) visitor(_sliver!);
   }
 
   @override
@@ -321,7 +315,7 @@ class SliverStickyHeaderRenderObjectElement extends RenderObjectElement {
   }
 
   @override
-  void mount(Element parent, dynamic newSlot) {
+  void mount(Element? parent, dynamic newSlot) {
     super.mount(parent, newSlot);
     _header = updateChild(_header, widget.header, 0);
     _sliver = updateChild(_sliver, widget.sliver, 1);
@@ -336,21 +330,23 @@ class SliverStickyHeaderRenderObjectElement extends RenderObjectElement {
   }
 
   @override
-  void insertChildRenderObject(RenderObject child, int slot) {
-    final RenderSliverStickyHeader renderObject = this.renderObject;
-    if (slot == 0) renderObject.header = child;
-    if (slot == 1) renderObject.child = child;
+  void insertRenderObjectChild(RenderObject child, int? slot) {
+    final RenderSliverStickyHeader renderObject =
+        this.renderObject as RenderSliverStickyHeader;
+    if (slot == 0) renderObject.header = child as RenderBox?;
+    if (slot == 1) renderObject.child = child as RenderSliver?;
     assert(renderObject == this.renderObject);
   }
 
   @override
-  void moveChildRenderObject(RenderObject child, slot) {
+  void moveRenderObjectChild(RenderObject child, slot, newSlot) {
     assert(false);
   }
 
   @override
-  void removeChildRenderObject(RenderObject child) {
-    final RenderSliverStickyHeader renderObject = this.renderObject;
+  void removeRenderObjectChild(RenderObject child, slot) {
+    final RenderSliverStickyHeader renderObject =
+        this.renderObject as RenderSliverStickyHeader;
     if (renderObject.header == child) renderObject.header = null;
     if (renderObject.child == child) renderObject.child = null;
     assert(renderObject == this.renderObject);
diff --git a/pubspec.yaml b/pubspec.yaml
index a5e665d..8443fb4 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,17 +1,17 @@
 name: flutter_sticky_header
 description: Flutter implementation of sticky headers as a sliver. Use it in a CustomScrollView.
-version: 0.5.0
+version: 0.6.0
 homepage: https://github.com/letsar/flutter_sticky_header
 
 dependencies:
   flutter:
     sdk: flutter
-  value_layout_builder: ^0.2.0
+  value_layout_builder: ^0.3.0
 
 dev_dependencies:
   flutter_test:
     sdk: flutter
 
 environment:
-  sdk: ">=2.2.0 <3.0.0"
-  flutter: ">=1.20.0 <2.0.0"
+  sdk: '>=2.12.0 <3.0.0'
+  flutter: '>=1.24.0-10.2.pre'
diff --git a/test/controller_test.dart b/test/controller_test.dart
index fbca4f0..827a979 100644
--- a/test/controller_test.dart
+++ b/test/controller_test.dart
@@ -5,7 +5,7 @@ import 'package:flutter_sticky_header/flutter_sticky_header.dart';
 
 void main() {
   setUp(() {
-    WidgetsBinding.instance.renderView.configuration =
+    WidgetsBinding.instance!.renderView.configuration =
         TestViewConfiguration(size: Size(400, 800));
   });
 
@@ -195,8 +195,8 @@ void main() {
 
 class _Header extends StatelessWidget {
   const _Header({
-    Key key,
-    @required this.index,
+    Key? key,
+    required this.index,
   }) : super(key: key);
 
   final int index;
@@ -213,7 +213,7 @@ class _Header extends StatelessWidget {
 
 class _Sliver extends StatelessWidget {
   const _Sliver({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -229,7 +229,7 @@ class _Sliver extends StatelessWidget {
 
 class _SliverItem extends StatelessWidget {
   const _SliverItem({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
diff --git a/test/sticky_test.dart b/test/sticky_test.dart
index f855154..4300734 100644
--- a/test/sticky_test.dart
+++ b/test/sticky_test.dart
@@ -5,7 +5,7 @@ import 'package:flutter_sticky_header/flutter_sticky_header.dart';
 
 void main() {
   setUp(() {
-    WidgetsBinding.instance.renderView.configuration =
+    WidgetsBinding.instance!.renderView.configuration =
         TestViewConfiguration(size: Size(400, 800));
   });
 
@@ -171,8 +171,8 @@ void main() {
 
 class _Header extends StatelessWidget {
   const _Header({
-    Key key,
-    @required this.index,
+    Key? key,
+    required this.index,
   }) : super(key: key);
 
   final int index;
@@ -189,7 +189,7 @@ class _Header extends StatelessWidget {
 
 class _Sliver extends StatelessWidget {
   const _Sliver({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -205,7 +205,7 @@ class _Sliver extends StatelessWidget {
 
 class _SliverItem extends StatelessWidget {
   const _SliverItem({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override