InputDecorationTheme.isCollapsed doesn't work if InputDecoration.isCollapsed is not provided. (#133189)

`appleDefault` method didn't include setting values for non-null (here `isCollapsed`) parameters initially, which has been updated and documented in this commit.

Existing and new tests are passing.

Fixes #133144

packages/flutter/lib/src/material/input_decorator.dart

@@ -2169,7 +2169,10 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
       return border.copyWith(
         borderSide: BorderSide(
           color: _getDefaultM2BorderColor(themeData),
-          width: (decoration.isCollapsed || decoration.border == InputBorder.none || !decoration.enabled)
+          width: (
+              (decoration.isCollapsed ?? themeData.inputDecorationTheme.isCollapsed)
+                  || decoration.border == InputBorder.none
+                  || !decoration.enabled)
             ? 0.0
             : isFocused ? 2.0 : 1.0,
         ),
@@ -2402,7 +2405,8 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
 
     final EdgeInsets contentPadding;
     final double floatingLabelHeight;
-    if (decoration.isCollapsed) {
+    if (decoration.isCollapsed
+        ?? themeData.inputDecorationTheme.isCollapsed) {
       floatingLabelHeight = 0.0;
       contentPadding = decorationContentPadding ?? EdgeInsets.zero;
     } else if (!border.isOutline) {
@@ -2430,7 +2434,7 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
     final _Decorator decorator = _Decorator(
       decoration: _Decoration(
         contentPadding: contentPadding,
-        isCollapsed: decoration.isCollapsed,
+        isCollapsed: decoration.isCollapsed ?? themeData.inputDecorationTheme.isCollapsed,
         floatingLabelHeight: floatingLabelHeight,
         floatingLabelAlignment: decoration.floatingLabelAlignment!,
         floatingLabelProgress: _floatingLabelAnimation.value,
@@ -2577,7 +2581,7 @@ class InputDecoration {
     this.errorMaxLines,
     this.floatingLabelBehavior,
     this.floatingLabelAlignment,
-    this.isCollapsed = false,
+    this.isCollapsed,
     this.isDense,
     this.contentPadding,
     this.prefixIcon,
@@ -2976,7 +2980,7 @@ class InputDecoration {
   /// A collapsed decoration cannot have [labelText], [errorText], an [icon].
   ///
   /// To create a collapsed input decoration, use [InputDecoration.collapsed].
-  final bool isCollapsed;
+  final bool? isCollapsed;
 
   /// An icon that appears before the [prefix] or [prefixText] and before
   /// the editable part of the text field, within the decoration's container.
@@ -3620,7 +3624,7 @@ class InputDecoration {
       floatingLabelAlignment: floatingLabelAlignment ?? theme.floatingLabelAlignment,
       isDense: isDense ?? theme.isDense,
       contentPadding: contentPadding ?? theme.contentPadding,
-      isCollapsed: isCollapsed,
+      isCollapsed: isCollapsed ?? theme.isCollapsed,
       iconColor: iconColor ?? theme.iconColor,
       prefixStyle: prefixStyle ?? theme.prefixStyle,
       prefixIconColor: prefixIconColor ?? theme.prefixIconColor,
@@ -3782,7 +3786,7 @@ class InputDecoration {
       if (floatingLabelAlignment != null) 'floatingLabelAlignment: $floatingLabelAlignment',
       if (isDense ?? false) 'isDense: $isDense',
       if (contentPadding != null) 'contentPadding: $contentPadding',
-      if (isCollapsed) 'isCollapsed: $isCollapsed',
+      if (isCollapsed ?? false) 'isCollapsed: $isCollapsed',
       if (prefixIcon != null) 'prefixIcon: $prefixIcon',
       if (prefixIconColor != null) 'prefixIconColor: $prefixIconColor',
       if (prefix != null) 'prefix: $prefix',

packages/flutter/test/material/input_decorator_test.dart

@@ -6570,4 +6570,25 @@ testWidgets('OutlineInputBorder with BorderRadius.zero should draw a rectangular
     expect(find.byType(InputDecorator), findsOneWidget);
     expect(tester.renderObject<RenderBox>(find.text('COUNTER')).size, Size.zero);
   });
+
+  group('isCollapsed parameter works with themeData', () {
+    test('parameter is provided in InputDecorationTheme', () {
+      final InputDecoration decoration = const InputDecoration(
+        hintText: 'Hello, Flutter!',
+      ).applyDefaults(const InputDecorationTheme(
+          isCollapsed: true,
+      ));
+
+      expect(decoration.isCollapsed, true);
+    });
+
+    test('parameter is provided in InputDecoration', () {
+      final InputDecoration decoration = const InputDecoration(
+        isCollapsed: true,
+        hintText: 'Hello, Flutter!',
+      ).applyDefaults(const InputDecorationTheme());
+
+      expect(decoration.isCollapsed, true);
+    });
+  });
 }