Handle nullable values with genericArgumentFactories (#826)

Fixes #803

Author: kevmoo

json_serializable/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 4.0.3-dev
+
+- Correctly handle nullable values with `genericArgumentFactories`.
+
 ## 4.0.2
 
 - Correctly handle nullable `Map` and `Iterable` JSON types exposed by both

json_serializable/lib/src/encoder_helper.dart

@@ -30,7 +30,7 @@ abstract class EncodeHelper implements HelperCore {
         final helperName = toJsonForType(
           arg.instantiate(nullabilitySuffix: NullabilitySuffix.none),
         );
-        buffer.write(',Object Function(${arg.name} value) $helperName');
+        buffer.write(',Object? Function(${arg.name} value) $helperName');
       }
       if (element.typeParameters.isNotEmpty) {
         buffer.write(',');

json_serializable/pubspec.yaml

@@ -1,11 +1,12 @@
 name: json_serializable
-version: 4.0.2
+version: 4.0.3-dev
 description: >-
   Automatically generate code for converting to and from JSON by annotating
   Dart classes.
 repository: https://github.com/google/json_serializable.dart/tree/master/json_serializable
 environment:
   # Keeping this <2.12.0 because the code is not null safe – yet!
+  # https://github.com/google/json_serializable.dart/issues/821
   sdk: '>=2.11.99 <3.0.0'
 
 dependencies:

json_serializable/test/generic_files/generic_argument_factories.dart

@@ -30,8 +30,8 @@ class GenericClassWithHelpers<T, S> {
       _$GenericClassWithHelpersFromJson(json, fromJsonT, fromJsonS);
 
   Map<String, dynamic> toJson(
-    Object Function(T value) toJsonT,
-    Object Function(S value) toJsonS,
+    Object? Function(T value) toJsonT,
+    Object? Function(S value) toJsonS,
   ) =>
       _$GenericClassWithHelpersToJson(this, toJsonT, toJsonS);
 }
@@ -42,7 +42,10 @@ class ConcreteClass {
 
   final GenericClassWithHelpers<double, BigInt> value2;
 
-  ConcreteClass(this.value, this.value2);
+  // Regression scenario for google/json_serializable.dart#803
+  final GenericClassWithHelpers<double?, BigInt?> value3;
+
+  ConcreteClass(this.value, this.value2, this.value3);
 
   factory ConcreteClass.fromJson(Map<String, dynamic> json) =>
       _$ConcreteClassFromJson(json);

json_serializable/test/generic_files/generic_argument_factories.g.dart

@@ -108,6 +108,56 @@ void main() {
   "someSet": [
    "2"
   ]
+ },
+ "value3": {
+  "value": 3.14,
+  "list": [
+   3.14
+  ],
+  "someSet": [
+   "2"
+  ]
+ }
+}''';
+
+      final instance = ConcreteClass.fromJson(
+        jsonDecode(inputJson) as Map<String, dynamic>,
+      );
+
+      expect(loudEncode(instance), inputJson);
+    });
+
+    test('round trip decode/decode with null', () {
+      const inputJson = r'''
+{
+ "value": {
+  "value": 5,
+  "list": [
+   5
+  ],
+  "someSet": [
+   "string"
+  ]
+ },
+ "value2": {
+  "value": 3.14,
+  "list": [
+   3.14
+  ],
+  "someSet": [
+   "2"
+  ]
+ },
+ "value3": {
+  "value": null,
+  "list": [
+   3.14,
+   null
+  ],
+  "someSet": [
+   "2",
+   null
+  ]
  }
 }''';