[file_selector] Return a non-null value from getSavePath on web (flutter#3630)

Author: stuartmorgan-g

packages/file_selector/file_selector_web/CHANGELOG.md

@@ -1,3 +1,8 @@
+# 0.8.1
+
+- Return a non-null value from `getSavePath` for consistency with
+  API expectations that null indicates canceling.
+
 # 0.8.0
 
 - Migrated to null-safety

packages/file_selector/file_selector_web/example/integration_test/file_selector_web_test.dart

@@ -73,6 +73,14 @@ void main() {
         expect(await files[1].lastModified(), isNotNull);
       });
     });
+
+    group('getSavePath', () {
+      testWidgets('returns non-null', (WidgetTester _) async {
+        final plugin = FileSelectorWeb();
+        final savePath = plugin.getSavePath();
+        expect(await savePath, isNotNull);
+      });
+    });
   });
 }
 

packages/file_selector/file_selector_web/lib/file_selector_web.dart

@@ -45,14 +45,17 @@ class FileSelectorWeb extends FileSelectorPlatform {
     return _openFiles(acceptedTypeGroups: acceptedTypeGroups, multiple: true);
   }
 
+  // This is intended to be passed to XFile, which ignores the path, but 'null'
+  // indicates a canceled save on other platforms, so provide a non-null dummy
+  // value.
   @override
   Future<String?> getSavePath({
     List<XTypeGroup>? acceptedTypeGroups,
     String? initialDirectory,
     String? suggestedName,
     String? confirmButtonText,
   }) async =>
-      null;
+      '';
 
   @override
   Future<String?> getDirectoryPath({

packages/file_selector/file_selector_web/pubspec.yaml

@@ -1,7 +1,7 @@
 name: file_selector_web
 description: Web platform implementation of file_selector
 homepage: https://github.com/flutter/plugins/tree/master/packages/file_selector/file_selector_web
-version: 0.8.0
+version: 0.8.1
 
 flutter:
   plugin: