Prevent concatenateUris from adding trailing redundant '?'. Add test …

…for `concatenateUris`

packages/go_router/lib/src/path_utils.dart

@@ -123,12 +123,19 @@ String concatenatePaths(String parentPath, String childPath) {
 ///
 /// e.g: pathA = /a?fid=f1, pathB = c/d?pid=p2,  concatenatePaths(pathA, pathB) = /a/c/d?fid=1&pid=2.
 Uri concatenateUris(Uri parentUri, Uri childUri) {
+  // Merge query parameters from both Uris. We don't return an empty map to prevent trailing '?'.
+  final Map<String, dynamic>? newParameters =
+      parentUri.queryParameters.isNotEmpty &&
+              childUri.queryParameters.isNotEmpty
+          ? <String, dynamic>{
+              ...parentUri.queryParameters,
+              ...childUri.queryParameters,
+            }
+          : null;
+
   final Uri newUri = parentUri.replace(
     path: concatenatePaths(parentUri.path, childUri.path),
-    queryParameters: <String, dynamic>{
-      ...parentUri.queryParameters,
-      ...childUri.queryParameters,
-    },
+    queryParameters: newParameters,
   );
 
   return newUri;

packages/go_router/test/path_utils_test.dart

@@ -93,6 +93,18 @@ void main() {
     verifyThrows('', '');
   });
 
+  test('concatenateUris', () {
+    void verify(String pathA, String pathB, String expected) {
+      final String result =
+          concatenateUris(Uri.parse(pathA), Uri.parse(pathB)).toString();
+      expect(result, expected);
+    }
+
+    verify('/a', 'b/c', '/a/b/c');
+    verify('/', 'b', '/b');
+    verify('/a?fid=f1', 'b/c?pid=p2', '/a/b/c?fid=f1&pid=p2');
+  });
+
   test('canonicalUri', () {
     void verify(String path, String expected) =>
         expect(canonicalUri(path), expected);