fix nullability issues (#67306)

packages/flutter/lib/src/animation/animations.dart

@@ -495,7 +495,7 @@ class TrainHoppingAnimation extends Animation<double>
       : assert(_currentTrain != null) {
     if (_nextTrain != null) {
       if (_currentTrain!.value == _nextTrain!.value) {
-        _currentTrain = _nextTrain!;
+        _currentTrain = _nextTrain;
         _nextTrain = null;
       } else if (_currentTrain!.value > _nextTrain!.value) {
         _mode = _TrainHoppingMode.maximize;
@@ -557,7 +557,7 @@ class TrainHoppingAnimation extends Animation<double>
         _currentTrain!
           ..removeStatusListener(_statusChangeHandler)
           ..removeListener(_valueChangeHandler);
-        _currentTrain = _nextTrain!;
+        _currentTrain = _nextTrain;
         _nextTrain = null;
         _currentTrain!.addStatusListener(_statusChangeHandler);
         _statusChangeHandler(_currentTrain!.status);

packages/flutter/lib/src/cupertino/picker.dart

@@ -186,7 +186,7 @@ class CupertinoPicker extends StatefulWidget {
   /// This can be called during scrolls and during ballistic flings. To get the
   /// value only when the scrolling settles, use a [NotificationListener],
   /// listen for [ScrollEndNotification] and read its [FixedExtentMetrics].
-  final ValueChanged<int> onSelectedItemChanged;
+  final ValueChanged<int>? onSelectedItemChanged;
 
   /// A delegate that lazily instantiates children.
   final ListWheelChildDelegate childDelegate;
@@ -247,7 +247,7 @@ class _CupertinoPickerState extends State<CupertinoPicker> {
     }
 
     if (widget.onSelectedItemChanged != null) {
-      widget.onSelectedItemChanged(index);
+      widget.onSelectedItemChanged!(index);
     }
   }
 

packages/flutter/lib/src/cupertino/tab_view.dart

@@ -172,7 +172,7 @@ class _CupertinoTabViewState extends State<CupertinoTabView> {
     WidgetBuilder? routeBuilder;
     String? title;
     if (name == Navigator.defaultRouteName && widget.builder != null) {
-      routeBuilder = widget.builder!;
+      routeBuilder = widget.builder;
       title = widget.defaultTitle;
     } else if (widget.routes != null) {
       routeBuilder = widget.routes![name];

packages/flutter/lib/src/rendering/paragraph.dart

@@ -46,7 +46,7 @@ class TextParentData extends ContainerBoxParentData<RenderBox> {
   @override
   String toString() {
     final List<String> values = <String>[
-      if (offset != null) 'offset=$offset',
+      'offset=$offset',
       if (scale != null) 'scale=$scale',
       super.toString(),
     ];
@@ -819,14 +819,12 @@ class RenderParagraph extends RenderBox
     String? workingLabel;
     for (final InlineSpanSemanticsInformation info in _semanticsInfo!) {
       if (info.requiresOwnNode) {
-        if (workingText != null) {
         combined.add(InlineSpanSemanticsInformation(
           workingText,
           semanticsLabel: workingLabel ?? workingText,
         ));
         workingText = '';
         workingLabel = null;
-        }
         combined.add(info);
       } else {
         workingText += info.text;
@@ -838,14 +836,10 @@ class RenderParagraph extends RenderBox
         }
       }
     }
-    if (workingText != null) {
     combined.add(InlineSpanSemanticsInformation(
       workingText,
       semanticsLabel: workingLabel,
     ));
-    } else { // ignore: dead_code
-      assert(workingLabel != null);
-    }
     return combined;
   }
 

packages/flutter/lib/src/rendering/proxy_box.dart

@@ -4481,7 +4481,6 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
   void describeSemanticsConfiguration(SemanticsConfiguration config) {
     super.describeSemanticsConfiguration(config);
     config.isSemanticBoundary = container;
-    if (explicitChildNodes != null)
     config.explicitChildNodes = explicitChildNodes;
     assert((scopesRoute == true && explicitChildNodes == true) || scopesRoute != true,
       'explicitChildNodes must be set to true if scopes route is true');

packages/flutter/lib/src/rendering/table.dart

@@ -1085,7 +1085,6 @@ class RenderTable extends RenderBox {
           final TableCellParentData childParentData = child.parentData! as TableCellParentData;
           switch (childParentData.verticalAlignment ?? defaultVerticalAlignment) {
             case TableCellVerticalAlignment.baseline:
-              if (baselines[x] != null)
               childParentData.offset = Offset(positions[x], rowTop + beforeBaselineDistance - baselines[x]);
               break;
             case TableCellVerticalAlignment.top:

packages/flutter/lib/src/semantics/semantics.dart

@@ -510,15 +510,7 @@ class _SemanticsDiagnosticableNode extends DiagnosticableNode<SemanticsNode> {
   final DebugSemanticsDumpOrder childOrder;
 
   @override
-  List<DiagnosticsNode> getChildren() {
-    if (value != null)
-      return value.debugDescribeChildren(childOrder: childOrder);
-
-    // `value` has a non-nullable return type, but might be null when
-    // running with weak checking, so we need to null check it above (and
-    // ignore the warning below that the null-handling logic is dead code).
-    return const <DiagnosticsNode>[]; // ignore: dead_code
-  }
+  List<DiagnosticsNode> getChildren() => value.debugDescribeChildren(childOrder: childOrder);
 }
 
 /// Provides hint values which override the default hints on supported
@@ -1419,12 +1411,10 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
       for (final SemanticsNode child in _children!)
         child._dead = true;
     }
-    if (newChildren != null) {
     for (final SemanticsNode child in newChildren) {
       assert(!child.isInvisible, 'Child $child is invisible and should not be added as a child of $this.');
       child._dead = false;
     }
-    }
     bool sawChange = false;
     if (_children != null) {
       for (final SemanticsNode child in _children!) {
@@ -1438,7 +1428,6 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
         }
       }
     }
-    if (newChildren != null) {
     for (final SemanticsNode child in newChildren) {
       if (child.parent != this) {
         if (child.parent != null) {
@@ -1454,7 +1443,6 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
         sawChange = true;
       }
     }
-    }
     if (!sawChange && _children != null) {
       assert(newChildren != null);
       assert(newChildren.length == _children!.length);
@@ -1966,10 +1954,8 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
           mergedTags ??= <SemanticsTag>{};
           mergedTags!.addAll(node.tags!);
         }
-        if (node._customSemanticsActions != null) {
         for (final CustomSemanticsAction action in _customSemanticsActions.keys)
           customSemanticsActionIds.add(CustomSemanticsAction.getIdentifier(action));
-        }
         if (node.hintOverrides != null) {
           if (node.hintOverrides!.onTapHint != null) {
             final CustomSemanticsAction action = CustomSemanticsAction.overridingAction(

packages/flutter/lib/src/services/text_input.dart

@@ -790,7 +790,7 @@ abstract class TextInputClient {
   const TextInputClient();
 
   /// The current state of the [TextEditingValue] held by this client.
-  TextEditingValue get currentTextEditingValue;
+  TextEditingValue? get currentTextEditingValue;
 
   /// The [AutofillScope] this [TextInputClient] belongs to, if any.
   ///
@@ -1164,7 +1164,7 @@ class TextInput {
     if (method == 'TextInputClient.requestExistingInputState') {
       assert(_currentConnection!._client != null);
       _attach(_currentConnection!, _currentConfiguration);
-      final TextEditingValue editingValue = _currentConnection!._client.currentTextEditingValue;
+      final TextEditingValue? editingValue = _currentConnection!._client.currentTextEditingValue;
       if (editingValue != null) {
         _setEditingState(editingValue);
       }

packages/flutter/lib/src/widgets/container.dart

@@ -105,12 +105,7 @@ class DecoratedBox extends SingleChildRenderObjectWidget {
         break;
     }
     properties.add(EnumProperty<DecorationPosition>('position', position, level: DiagnosticLevel.hidden));
-    properties.add(DiagnosticsProperty<Decoration>(
-      label,
-      decoration,
-      ifNull: 'no decoration',
-      showName: decoration != null,
-    ));
+    properties.add(DiagnosticsProperty<Decoration>(label, decoration));
   }
 }
 

packages/flutter/lib/src/widgets/focus_scope.dart

@@ -527,9 +527,7 @@ class _FocusState extends State<Focus> {
       // _createNode is overridden in _FocusScopeState.
       _internalNode ??= _createNode();
     }
-    if (widget.descendantsAreFocusable != null) {
     focusNode.descendantsAreFocusable = widget.descendantsAreFocusable;
-    }
     if (widget.skipTraversal != null) {
       focusNode.skipTraversal = widget.skipTraversal!;
     }
@@ -615,9 +613,7 @@ class _FocusState extends State<Focus> {
       if (widget.canRequestFocus != null) {
         focusNode.canRequestFocus = widget.canRequestFocus!;
       }
-      if (widget.descendantsAreFocusable != null) {
       focusNode.descendantsAreFocusable = widget.descendantsAreFocusable;
-      }
     } else {
       _focusAttachment!.detach();
       focusNode.removeListener(_handleFocusChanged);

packages/flutter/lib/src/widgets/layout_builder.dart

@@ -116,8 +116,7 @@ class _LayoutBuilderElement<ConstraintType extends Constraints> extends RenderOb
 
   void _layout(ConstraintType constraints) {
     owner!.buildScope(this, () {
-      Widget? built;
-      if (widget.builder != null) {
+      Widget built;
       try {
         built = widget.builder(this, constraints);
         debugWidgetBuilderValue(widget, built);
@@ -133,7 +132,6 @@ class _LayoutBuilderElement<ConstraintType extends Constraints> extends RenderOb
           ),
         );
       }
-      }
       try {
         _child = updateChild(_child, built, null);
         assert(_child != null);

packages/flutter/lib/src/widgets/navigator.dart

@@ -3603,11 +3603,11 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
         assert(previousOldPageRouteEntry != null);
         final List<_RouteEntry> pagelessRoutes = pageRouteToPagelessRoutes
           .putIfAbsent(
-            previousOldPageRouteEntry!,
+            previousOldPageRouteEntry,
             () => <_RouteEntry>[],
           );
         pagelessRoutes.add(potentialEntryToRemove);
-        if (previousOldPageRouteEntry.isWaitingForExitingDecision)
+        if (previousOldPageRouteEntry!.isWaitingForExitingDecision)
           potentialEntryToRemove.markNeedsExitingDecision();
         continue;
       }
@@ -3651,7 +3651,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
         assert(previousOldPageRouteEntry != null);
         final List<_RouteEntry> pagelessRoutes = pageRouteToPagelessRoutes
           .putIfAbsent(
-          previousOldPageRouteEntry!,
+          previousOldPageRouteEntry,
             () => <_RouteEntry>[]
         );
         pagelessRoutes.add(oldEntry);

packages/flutter/lib/src/widgets/nested_scroll_view.dart

@@ -808,10 +808,7 @@ class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldCont
     return false;
   }
 
-  void updateShadow() {
-    if (_onHasScrolledBodyChanged != null)
-      _onHasScrolledBodyChanged();
-  }
+  void updateShadow() { _onHasScrolledBodyChanged(); }
 
   ScrollDirection get userScrollDirection => _userScrollDirection;
   ScrollDirection _userScrollDirection = ScrollDirection.idle;

packages/flutter/lib/src/widgets/sliver.dart

@@ -1107,7 +1107,7 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
           if (childParentData != null)
             childParentData.layoutOffset = null;
 
-          newChildren[newIndex] = _childElements[index]!;
+          newChildren[newIndex] = _childElements[index];
           // We need to make sure the original index gets processed.
           newChildren.putIfAbsent(index, () => null);
           // We do not want the remapped child to get deactivated during processElement.

packages/flutter/lib/src/widgets/widget_inspector.dart

@@ -970,7 +970,7 @@ mixin WidgetInspectorService {
   void initServiceExtensions(_RegisterServiceExtensionCallback registerServiceExtensionCallback) {
     _structuredExceptionHandler = _reportError;
     if (isStructuredErrorsEnabled()) {
-      FlutterError.onError = _structuredExceptionHandler!;
+      FlutterError.onError = _structuredExceptionHandler;
     }
     _registerServiceExtensionCallback = registerServiceExtensionCallback;
     assert(!_debugServiceExtensionsRegistered);
@@ -2284,11 +2284,9 @@ class _WidgetInspectorState extends State<WidgetInspector>
     if (_lastPointerLocation != null) {
       _inspectAt(_lastPointerLocation!);
 
-      if (selection != null) {
       // Notify debuggers to open an inspector on the object.
       developer.inspect(selection.current);
     }
-    }
     setState(() {
       // Only exit select mode if there is a button to return to select mode.
       if (widget.selectButtonBuilder != null)