Remove exclamation marks (#107683)

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

@@ -2152,7 +2152,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
 
   @override
   void performPrivateCommand(String action, Map<String, dynamic> data) {
-    widget.onAppPrivateCommand!(action, data);
+    widget.onAppPrivateCommand?.call(action, data);
   }
 
   // The original position of the caret on FloatingCursorDragState.start.

packages/flutter/test/widgets/editable_text_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:convert' show jsonDecode;
 import 'dart:ui' as ui;
 
 import 'package:flutter/cupertino.dart';
@@ -397,6 +398,53 @@ void main() {
     );
   });
 
+  testWidgets('onAppPrivateCommand does not throw', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MediaQuery(
+        data: const MediaQueryData(),
+        child: Directionality(
+          textDirection: TextDirection.ltr,
+          child: FocusScope(
+            node: focusScopeNode,
+            autofocus: true,
+            child: EditableText(
+              backgroundCursorColor: Colors.grey,
+              controller: controller,
+              focusNode: focusNode,
+              style: textStyle,
+              cursorColor: cursorColor,
+            ),
+          ),
+        ),
+      ),
+    );
+
+    await tester.tap(find.byType(EditableText));
+    await tester.showKeyboard(find.byType(EditableText));
+    controller.text = 'test';
+    await tester.idle();
+
+    final ByteData? messageBytes = const JSONMessageCodec().encodeMessage(<String, dynamic>{
+      'args': <dynamic>[
+        -1, // The magic clint id that points to the current client.
+        jsonDecode('{"action": "actionCommand", "data": {"input_context" : "abcdefg"}}'),
+      ],
+      'method': 'TextInputClient.performPrivateCommand',
+    });
+
+    Object? error;
+    try {
+      await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage(
+        'flutter/textinput',
+        messageBytes,
+        (ByteData? _) {},
+      );
+    } catch (e) {
+      error = e;
+    }
+    expect(error, isNull);
+  });
+
   group('Infer keyboardType from autofillHints', () {
     testWidgets(
       'infer keyboard types from autofillHints: ios',