diff --git a/example/lib/auth_client.dart b/example/lib/auth_client.dart
new file mode 100644
index 000000000..0cf926c39
--- /dev/null
+++ b/example/lib/auth_client.dart
@@ -0,0 +1,38 @@
+import 'package:dio/dio.dart';
+import 'package:retrofit/retrofit.dart';
+
+part 'auth_client.g.dart';
+
+@RestApi()
+abstract class AuthClient {
+  factory AuthClient(Dio dio, {String? baseUrl}) = RestClientYmlp;
+
+  @POST('/api/auth/mqttClient/authentication')
+  Future<Object?> authenticationUsingPost({
+    @Body() required RegisterModel submitModel,
+  });
+}
+
+class RegisterModel {
+  const RegisterModel({
+    this.channel,
+    this.mobile,
+    this.verfiyCode,
+  });
+
+  factory RegisterModel.fromJson(Map<String, Object?> json) => RegisterModel(
+        channel: json['channel'] as String?,
+        mobile: json['mobile'] as String?,
+        verfiyCode: json['verfiyCode'] as String?,
+      );
+
+  final String? channel;
+  final String? mobile;
+  final String? verfiyCode;
+
+  Map<String, dynamic> toJson() => <String, dynamic>{
+        'channel': channel,
+        'mobile': mobile,
+        'verfiyCode': verfiyCode,
+      };
+}
diff --git a/generator/CHANGELOG.md b/generator/CHANGELOG.md
index b842163c2..136cbba5d 100644
--- a/generator/CHANGELOG.md
+++ b/generator/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## 8.0.2
+
+- fix #630 Null check operator used on a null value
+
 ## 8.0.1
 
 - Add option class-name to customize the name of retrofit generator
@@ -10,6 +14,7 @@
 - Add PreventNullToAbsent annotation to allow null sent to server
 
 ## 7.0.8
+
 - Use `toJson()` instead of `.name` if enums have `toJson()`.
 
 ## 7.0.7
@@ -20,6 +25,7 @@
 ## 7.0.6
 
 - Fix DateTime.toIso8601String() issue #586
+
 ## 7.0.3
 
 - Add support for analyzer 6.0.0
diff --git a/generator/lib/src/generator.dart b/generator/lib/src/generator.dart
index de3691f7c..35cf5e920 100644
--- a/generator/lib/src/generator.dart
+++ b/generator/lib/src/generator.dart
@@ -849,7 +849,7 @@ You should create a new class to encapsulate the response.
                   )
                   .statement,
             );
-        } else if (returnType.toString() == 'dynamic') {
+        } else if (returnType is DynamicType || returnType.isDartCoreObject) {
           blocks
             ..add(
               declareFinal(_resultVar)