diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartClientCodegen.java
index 589ef137f34..b26f23891c0 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartClientCodegen.java
@@ -64,6 +64,7 @@ public class DartClientCodegen extends AbstractDartCodegen {
 
         final String libFolder = sourceFolder + File.separator + "lib";
         supportingFiles.add(new SupportingFile("pubspec.mustache", "", "pubspec.yaml"));
+        supportingFiles.add(new SupportingFile("analysis_options.mustache", "", "analysis_options.yaml"));
         supportingFiles.add(new SupportingFile("api_client.mustache", libFolder, "api_client.dart"));
         supportingFiles.add(new SupportingFile("api_exception.mustache", libFolder, "api_exception.dart"));
         supportingFiles.add(new SupportingFile("api_helper.mustache", libFolder, "api_helper.dart"));
diff --git a/modules/openapi-generator/src/main/resources/dart2/analysis_options.mustache b/modules/openapi-generator/src/main/resources/dart2/analysis_options.mustache
new file mode 100644
index 00000000000..83d5a10bd7b
--- /dev/null
+++ b/modules/openapi-generator/src/main/resources/dart2/analysis_options.mustache
@@ -0,0 +1,3 @@
+analyzer:
+  strong-mode:
+    implicit-casts: true
diff --git a/modules/openapi-generator/src/main/resources/dart2/api_client.mustache b/modules/openapi-generator/src/main/resources/dart2/api_client.mustache
index f3af060d514..d7f90713d5f 100644
--- a/modules/openapi-generator/src/main/resources/dart2/api_client.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/api_client.mustache
@@ -65,7 +65,7 @@ class ApiClient {
   Future<Response> invokeAPI(
     String path,
     String method,
-    Iterable<QueryParam> queryParams,
+    List<QueryParam> queryParams,
     Object body,
     Map<String, String> headerParams,
     Map<String, String> formParams,
@@ -177,13 +177,13 @@ class ApiClient {
     List<QueryParam> queryParams,
     Map<String, String> headerParams,
   ) {
-    authNames.forEach((authName) {
+    for(final authName in authNames) {
       final auth = _authentications[authName];
       if (auth == null) {
         throw ArgumentError('Authentication undefined: $authName');
       }
       auth.applyToParams(queryParams, headerParams);
-    });
+    }
   }
 
 {{#native_serialization}}
diff --git a/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache b/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache
index 0e4520d3e98..1d599915a0a 100644
--- a/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache
@@ -132,9 +132,19 @@ class {{{classname}}} {
               {{/items.complexType}}
           {{/items.isArray}}
           {{^items.isArray}}
+              {{#items.isMap}}
         {{{name}}}: json[r'{{{baseName}}}'] == null
           ? null
-          : {{{complexType}}}.mapFromJson(json[r'{{{baseName}}}']),
+            {{#items.complexType}}
+          : {{items.complexType}}.mapFromJson(json[r'{{{baseName}}}']),
+            {{/items.complexType}}
+            {{^items.complexType}}
+          : (json[r'{{{baseName}}}'] as Map).cast<String, Map>(),
+            {{/items.complexType}}
+          {{/items.isMap}}
+          {{^items.isMap}}
+            {{{name}}}: json[r'{{{baseName}}}']
+          {{/items.isMap}}
           {{/items.isArray}}
         {{/isMap}}
         {{^isMap}}
@@ -189,12 +199,12 @@ class {{{classname}}} {
   static List<{{{classname}}}> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <{{{classname}}}>[]
-      : json.map((v) => {{{classname}}}.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => {{{classname}}}.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, {{{classname}}}> mapFromJson(Map<String, dynamic> json) {
     final map = <String, {{{classname}}}>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = {{{classname}}}.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = {{{classname}}}.fromJson(value));
     }
     return map;
   }
@@ -202,9 +212,9 @@ class {{{classname}}} {
   // maps a json object with a list of {{{classname}}}-objects as value to a dart map
   static Map<String, List<{{{classname}}}>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<{{{classname}}}>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = {{{classname}}}.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = {{{classname}}}.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/.openapi-generator/FILES b/samples/openapi3/client/petstore/dart2/petstore_client_lib/.openapi-generator/FILES
index 7cc5afea821..733ecbe3062 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/.openapi-generator/FILES
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/.openapi-generator/FILES
@@ -1,6 +1,7 @@
 .gitignore
 .travis.yml
 README.md
+analysis_options.yaml
 doc/ApiResponse.md
 doc/Category.md
 doc/Order.md
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/analysis_options.yaml b/samples/openapi3/client/petstore/dart2/petstore_client_lib/analysis_options.yaml
new file mode 100644
index 00000000000..83d5a10bd7b
--- /dev/null
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/analysis_options.yaml
@@ -0,0 +1,3 @@
+analyzer:
+  strong-mode:
+    implicit-casts: true
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api_client.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api_client.dart
index 35b984b86a1..37b6acfd4c6 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api_client.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api_client.dart
@@ -58,7 +58,7 @@ class ApiClient {
   Future<Response> invokeAPI(
     String path,
     String method,
-    Iterable<QueryParam> queryParams,
+    List<QueryParam> queryParams,
     Object body,
     Map<String, String> headerParams,
     Map<String, String> formParams,
@@ -168,13 +168,13 @@ class ApiClient {
     List<QueryParam> queryParams,
     Map<String, String> headerParams,
   ) {
-    authNames.forEach((authName) {
+    for(final authName in authNames) {
       final auth = _authentications[authName];
       if (auth == null) {
         throw ArgumentError('Authentication undefined: $authName');
       }
       auth.applyToParams(queryParams, headerParams);
-    });
+    }
   }
 
   static dynamic _deserialize(dynamic value, String targetType, {bool growable}) {
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/api_response.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/api_response.dart
index bd80caff35c..6bb070b7eeb 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/api_response.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/api_response.dart
@@ -65,12 +65,12 @@ class ApiResponse {
   static List<ApiResponse> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <ApiResponse>[]
-      : json.map((v) => ApiResponse.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => ApiResponse.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, ApiResponse> mapFromJson(Map<String, dynamic> json) {
     final map = <String, ApiResponse>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = ApiResponse.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = ApiResponse.fromJson(value));
     }
     return map;
   }
@@ -78,9 +78,9 @@ class ApiResponse {
   // maps a json object with a list of ApiResponse-objects as value to a dart map
   static Map<String, List<ApiResponse>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<ApiResponse>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = ApiResponse.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = ApiResponse.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/category.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/category.dart
index c63ffb1734f..c1c25b5a078 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/category.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/category.dart
@@ -56,12 +56,12 @@ class Category {
   static List<Category> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Category>[]
-      : json.map((v) => Category.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Category.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Category> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Category>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Category.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Category.fromJson(value));
     }
     return map;
   }
@@ -69,9 +69,9 @@ class Category {
   // maps a json object with a list of Category-objects as value to a dart map
   static Map<String, List<Category>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Category>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Category.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Category.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/order.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/order.dart
index a7b01582664..4cf8b636f47 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/order.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/order.dart
@@ -95,12 +95,12 @@ class Order {
   static List<Order> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Order>[]
-      : json.map((v) => Order.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Order.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Order> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Order>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Order.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Order.fromJson(value));
     }
     return map;
   }
@@ -108,9 +108,9 @@ class Order {
   // maps a json object with a list of Order-objects as value to a dart map
   static Map<String, List<Order>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Order>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Order.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Order.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart
index ee8c7615986..267e1485b8b 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart
@@ -91,12 +91,12 @@ class Pet {
   static List<Pet> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Pet>[]
-      : json.map((v) => Pet.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Pet.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Pet> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Pet>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Pet.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Pet.fromJson(value));
     }
     return map;
   }
@@ -104,9 +104,9 @@ class Pet {
   // maps a json object with a list of Pet-objects as value to a dart map
   static Map<String, List<Pet>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Pet>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Pet.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Pet.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/tag.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/tag.dart
index 63132f08a3a..0cd372910b9 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/tag.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/tag.dart
@@ -56,12 +56,12 @@ class Tag {
   static List<Tag> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Tag>[]
-      : json.map((v) => Tag.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Tag.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Tag> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Tag>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Tag.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Tag.fromJson(value));
     }
     return map;
   }
@@ -69,9 +69,9 @@ class Tag {
   // maps a json object with a list of Tag-objects as value to a dart map
   static Map<String, List<Tag>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Tag>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Tag.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Tag.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/user.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/user.dart
index bb512af491f..0eb3716fceb 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/user.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/user.dart
@@ -111,12 +111,12 @@ class User {
   static List<User> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <User>[]
-      : json.map((v) => User.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => User.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, User> mapFromJson(Map<String, dynamic> json) {
     final map = <String, User>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = User.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = User.fromJson(value));
     }
     return map;
   }
@@ -124,9 +124,9 @@ class User {
   // maps a json object with a list of User-objects as value to a dart map
   static Map<String, List<User>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<User>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = User.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = User.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/.openapi-generator/FILES b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/.openapi-generator/FILES
index 80d5a3a8fc8..a5fe5c494d6 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/.openapi-generator/FILES
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/.openapi-generator/FILES
@@ -1,6 +1,7 @@
 .gitignore
 .travis.yml
 README.md
+analysis_options.yaml
 doc/AdditionalPropertiesClass.md
 doc/Animal.md
 doc/AnotherFakeApi.md
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/analysis_options.yaml b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/analysis_options.yaml
new file mode 100644
index 00000000000..83d5a10bd7b
--- /dev/null
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/analysis_options.yaml
@@ -0,0 +1,3 @@
+analyzer:
+  strong-mode:
+    implicit-casts: true
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api_client.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api_client.dart
index 0aa83cf0197..cac7efad3bb 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api_client.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api_client.dart
@@ -61,7 +61,7 @@ class ApiClient {
   Future<Response> invokeAPI(
     String path,
     String method,
-    Iterable<QueryParam> queryParams,
+    List<QueryParam> queryParams,
     Object body,
     Map<String, String> headerParams,
     Map<String, String> formParams,
@@ -171,13 +171,13 @@ class ApiClient {
     List<QueryParam> queryParams,
     Map<String, String> headerParams,
   ) {
-    authNames.forEach((authName) {
+    for(final authName in authNames) {
       final auth = _authentications[authName];
       if (auth == null) {
         throw ArgumentError('Authentication undefined: $authName');
       }
       auth.applyToParams(queryParams, headerParams);
-    });
+    }
   }
 
   static dynamic _deserialize(dynamic value, String targetType, {bool growable}) {
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/additional_properties_class.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/additional_properties_class.dart
index 9e021e550b0..b62ac79d3e2 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/additional_properties_class.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/additional_properties_class.dart
@@ -54,18 +54,18 @@ class AdditionalPropertiesClass {
           (json[r'map_property'] as Map).cast<String, String>(),
         mapOfMapProperty: json[r'map_of_map_property'] == null
           ? null
-          : Map.mapFromJson(json[r'map_of_map_property']),
+          : (json[r'map_of_map_property'] as Map).cast<String, Map>(),
     );
 
   static List<AdditionalPropertiesClass> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <AdditionalPropertiesClass>[]
-      : json.map((v) => AdditionalPropertiesClass.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => AdditionalPropertiesClass.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, AdditionalPropertiesClass> mapFromJson(Map<String, dynamic> json) {
     final map = <String, AdditionalPropertiesClass>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = AdditionalPropertiesClass.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = AdditionalPropertiesClass.fromJson(value));
     }
     return map;
   }
@@ -73,9 +73,9 @@ class AdditionalPropertiesClass {
   // maps a json object with a list of AdditionalPropertiesClass-objects as value to a dart map
   static Map<String, List<AdditionalPropertiesClass>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<AdditionalPropertiesClass>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = AdditionalPropertiesClass.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = AdditionalPropertiesClass.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/animal.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/animal.dart
index 9786d8358b2..ba9066e4ef7 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/animal.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/animal.dart
@@ -54,12 +54,12 @@ class Animal {
   static List<Animal> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Animal>[]
-      : json.map((v) => Animal.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Animal.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Animal> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Animal>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Animal.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Animal.fromJson(value));
     }
     return map;
   }
@@ -67,9 +67,9 @@ class Animal {
   // maps a json object with a list of Animal-objects as value to a dart map
   static Map<String, List<Animal>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Animal>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Animal.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Animal.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/api_response.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/api_response.dart
index bd80caff35c..6bb070b7eeb 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/api_response.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/api_response.dart
@@ -65,12 +65,12 @@ class ApiResponse {
   static List<ApiResponse> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <ApiResponse>[]
-      : json.map((v) => ApiResponse.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => ApiResponse.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, ApiResponse> mapFromJson(Map<String, dynamic> json) {
     final map = <String, ApiResponse>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = ApiResponse.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = ApiResponse.fromJson(value));
     }
     return map;
   }
@@ -78,9 +78,9 @@ class ApiResponse {
   // maps a json object with a list of ApiResponse-objects as value to a dart map
   static Map<String, List<ApiResponse>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<ApiResponse>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = ApiResponse.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = ApiResponse.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_array_of_number_only.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_array_of_number_only.dart
index 7dac34b25c1..90ec9124de9 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_array_of_number_only.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_array_of_number_only.dart
@@ -51,12 +51,12 @@ class ArrayOfArrayOfNumberOnly {
   static List<ArrayOfArrayOfNumberOnly> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <ArrayOfArrayOfNumberOnly>[]
-      : json.map((v) => ArrayOfArrayOfNumberOnly.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => ArrayOfArrayOfNumberOnly.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, ArrayOfArrayOfNumberOnly> mapFromJson(Map<String, dynamic> json) {
     final map = <String, ArrayOfArrayOfNumberOnly>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = ArrayOfArrayOfNumberOnly.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = ArrayOfArrayOfNumberOnly.fromJson(value));
     }
     return map;
   }
@@ -64,9 +64,9 @@ class ArrayOfArrayOfNumberOnly {
   // maps a json object with a list of ArrayOfArrayOfNumberOnly-objects as value to a dart map
   static Map<String, List<ArrayOfArrayOfNumberOnly>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<ArrayOfArrayOfNumberOnly>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = ArrayOfArrayOfNumberOnly.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = ArrayOfArrayOfNumberOnly.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_number_only.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_number_only.dart
index 7a1de48923a..19b93cc3d73 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_number_only.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_number_only.dart
@@ -49,12 +49,12 @@ class ArrayOfNumberOnly {
   static List<ArrayOfNumberOnly> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <ArrayOfNumberOnly>[]
-      : json.map((v) => ArrayOfNumberOnly.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => ArrayOfNumberOnly.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, ArrayOfNumberOnly> mapFromJson(Map<String, dynamic> json) {
     final map = <String, ArrayOfNumberOnly>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = ArrayOfNumberOnly.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = ArrayOfNumberOnly.fromJson(value));
     }
     return map;
   }
@@ -62,9 +62,9 @@ class ArrayOfNumberOnly {
   // maps a json object with a list of ArrayOfNumberOnly-objects as value to a dart map
   static Map<String, List<ArrayOfNumberOnly>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<ArrayOfNumberOnly>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = ArrayOfNumberOnly.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = ArrayOfNumberOnly.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_test.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_test.dart
index 55b131a9e57..c911626fa13 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_test.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_test.dart
@@ -75,12 +75,12 @@ class ArrayTest {
   static List<ArrayTest> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <ArrayTest>[]
-      : json.map((v) => ArrayTest.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => ArrayTest.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, ArrayTest> mapFromJson(Map<String, dynamic> json) {
     final map = <String, ArrayTest>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = ArrayTest.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = ArrayTest.fromJson(value));
     }
     return map;
   }
@@ -88,9 +88,9 @@ class ArrayTest {
   // maps a json object with a list of ArrayTest-objects as value to a dart map
   static Map<String, List<ArrayTest>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<ArrayTest>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = ArrayTest.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = ArrayTest.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/capitalization.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/capitalization.dart
index afab73b9769..7b60d37fd39 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/capitalization.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/capitalization.dart
@@ -93,12 +93,12 @@ class Capitalization {
   static List<Capitalization> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Capitalization>[]
-      : json.map((v) => Capitalization.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Capitalization.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Capitalization> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Capitalization>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Capitalization.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Capitalization.fromJson(value));
     }
     return map;
   }
@@ -106,9 +106,9 @@ class Capitalization {
   // maps a json object with a list of Capitalization-objects as value to a dart map
   static Map<String, List<Capitalization>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Capitalization>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Capitalization.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Capitalization.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/cat.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/cat.dart
index 704152151d8..94d0b96a9c7 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/cat.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/cat.dart
@@ -63,12 +63,12 @@ class Cat {
   static List<Cat> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Cat>[]
-      : json.map((v) => Cat.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Cat.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Cat> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Cat>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Cat.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Cat.fromJson(value));
     }
     return map;
   }
@@ -76,9 +76,9 @@ class Cat {
   // maps a json object with a list of Cat-objects as value to a dart map
   static Map<String, List<Cat>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Cat>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Cat.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Cat.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/cat_all_of.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/cat_all_of.dart
index 307e777da3d..e3fe4944874 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/cat_all_of.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/cat_all_of.dart
@@ -47,12 +47,12 @@ class CatAllOf {
   static List<CatAllOf> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <CatAllOf>[]
-      : json.map((v) => CatAllOf.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => CatAllOf.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, CatAllOf> mapFromJson(Map<String, dynamic> json) {
     final map = <String, CatAllOf>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = CatAllOf.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = CatAllOf.fromJson(value));
     }
     return map;
   }
@@ -60,9 +60,9 @@ class CatAllOf {
   // maps a json object with a list of CatAllOf-objects as value to a dart map
   static Map<String, List<CatAllOf>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<CatAllOf>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = CatAllOf.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = CatAllOf.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/category.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/category.dart
index 59249c157a0..eddc54e7315 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/category.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/category.dart
@@ -54,12 +54,12 @@ class Category {
   static List<Category> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Category>[]
-      : json.map((v) => Category.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Category.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Category> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Category>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Category.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Category.fromJson(value));
     }
     return map;
   }
@@ -67,9 +67,9 @@ class Category {
   // maps a json object with a list of Category-objects as value to a dart map
   static Map<String, List<Category>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Category>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Category.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Category.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/class_model.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/class_model.dart
index 9192701eafd..927f01e06b6 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/class_model.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/class_model.dart
@@ -47,12 +47,12 @@ class ClassModel {
   static List<ClassModel> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <ClassModel>[]
-      : json.map((v) => ClassModel.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => ClassModel.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, ClassModel> mapFromJson(Map<String, dynamic> json) {
     final map = <String, ClassModel>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = ClassModel.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = ClassModel.fromJson(value));
     }
     return map;
   }
@@ -60,9 +60,9 @@ class ClassModel {
   // maps a json object with a list of ClassModel-objects as value to a dart map
   static Map<String, List<ClassModel>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<ClassModel>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = ClassModel.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = ClassModel.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/dog.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/dog.dart
index eb08c1e227c..3a1efcb1c4f 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/dog.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/dog.dart
@@ -63,12 +63,12 @@ class Dog {
   static List<Dog> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Dog>[]
-      : json.map((v) => Dog.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Dog.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Dog> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Dog>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Dog.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Dog.fromJson(value));
     }
     return map;
   }
@@ -76,9 +76,9 @@ class Dog {
   // maps a json object with a list of Dog-objects as value to a dart map
   static Map<String, List<Dog>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Dog>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Dog.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Dog.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/dog_all_of.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/dog_all_of.dart
index 0199b8707d1..a77ba88b0bf 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/dog_all_of.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/dog_all_of.dart
@@ -47,12 +47,12 @@ class DogAllOf {
   static List<DogAllOf> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <DogAllOf>[]
-      : json.map((v) => DogAllOf.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => DogAllOf.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, DogAllOf> mapFromJson(Map<String, dynamic> json) {
     final map = <String, DogAllOf>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = DogAllOf.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = DogAllOf.fromJson(value));
     }
     return map;
   }
@@ -60,9 +60,9 @@ class DogAllOf {
   // maps a json object with a list of DogAllOf-objects as value to a dart map
   static Map<String, List<DogAllOf>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<DogAllOf>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = DogAllOf.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = DogAllOf.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/enum_arrays.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/enum_arrays.dart
index f0e7b2417db..dc994bc308a 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/enum_arrays.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/enum_arrays.dart
@@ -56,12 +56,12 @@ class EnumArrays {
   static List<EnumArrays> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <EnumArrays>[]
-      : json.map((v) => EnumArrays.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => EnumArrays.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, EnumArrays> mapFromJson(Map<String, dynamic> json) {
     final map = <String, EnumArrays>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = EnumArrays.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = EnumArrays.fromJson(value));
     }
     return map;
   }
@@ -69,9 +69,9 @@ class EnumArrays {
   // maps a json object with a list of EnumArrays-objects as value to a dart map
   static Map<String, List<EnumArrays>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<EnumArrays>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = EnumArrays.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = EnumArrays.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/enum_test.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/enum_test.dart
index ae432599c99..51a444f1cea 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/enum_test.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/enum_test.dart
@@ -108,12 +108,12 @@ class EnumTest {
   static List<EnumTest> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <EnumTest>[]
-      : json.map((v) => EnumTest.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => EnumTest.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, EnumTest> mapFromJson(Map<String, dynamic> json) {
     final map = <String, EnumTest>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = EnumTest.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = EnumTest.fromJson(value));
     }
     return map;
   }
@@ -121,9 +121,9 @@ class EnumTest {
   // maps a json object with a list of EnumTest-objects as value to a dart map
   static Map<String, List<EnumTest>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<EnumTest>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = EnumTest.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = EnumTest.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/file_schema_test_class.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/file_schema_test_class.dart
index fb5f7593554..4f659cddafa 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/file_schema_test_class.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/file_schema_test_class.dart
@@ -56,12 +56,12 @@ class FileSchemaTestClass {
   static List<FileSchemaTestClass> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <FileSchemaTestClass>[]
-      : json.map((v) => FileSchemaTestClass.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => FileSchemaTestClass.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, FileSchemaTestClass> mapFromJson(Map<String, dynamic> json) {
     final map = <String, FileSchemaTestClass>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = FileSchemaTestClass.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = FileSchemaTestClass.fromJson(value));
     }
     return map;
   }
@@ -69,9 +69,9 @@ class FileSchemaTestClass {
   // maps a json object with a list of FileSchemaTestClass-objects as value to a dart map
   static Map<String, List<FileSchemaTestClass>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<FileSchemaTestClass>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = FileSchemaTestClass.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = FileSchemaTestClass.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/foo.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/foo.dart
index 19994af4cfe..4100fa1fa04 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/foo.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/foo.dart
@@ -47,12 +47,12 @@ class Foo {
   static List<Foo> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Foo>[]
-      : json.map((v) => Foo.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Foo.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Foo> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Foo>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Foo.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Foo.fromJson(value));
     }
     return map;
   }
@@ -60,9 +60,9 @@ class Foo {
   // maps a json object with a list of Foo-objects as value to a dart map
   static Map<String, List<Foo>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Foo>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Foo.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Foo.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/format_test.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/format_test.dart
index f0f2236ba88..5f735c24f86 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/format_test.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/format_test.dart
@@ -192,12 +192,12 @@ class FormatTest {
   static List<FormatTest> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <FormatTest>[]
-      : json.map((v) => FormatTest.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => FormatTest.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, FormatTest> mapFromJson(Map<String, dynamic> json) {
     final map = <String, FormatTest>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = FormatTest.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = FormatTest.fromJson(value));
     }
     return map;
   }
@@ -205,9 +205,9 @@ class FormatTest {
   // maps a json object with a list of FormatTest-objects as value to a dart map
   static Map<String, List<FormatTest>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<FormatTest>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = FormatTest.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = FormatTest.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/has_only_read_only.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/has_only_read_only.dart
index 2054a4594f3..dee44032840 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/has_only_read_only.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/has_only_read_only.dart
@@ -56,12 +56,12 @@ class HasOnlyReadOnly {
   static List<HasOnlyReadOnly> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <HasOnlyReadOnly>[]
-      : json.map((v) => HasOnlyReadOnly.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => HasOnlyReadOnly.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, HasOnlyReadOnly> mapFromJson(Map<String, dynamic> json) {
     final map = <String, HasOnlyReadOnly>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = HasOnlyReadOnly.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = HasOnlyReadOnly.fromJson(value));
     }
     return map;
   }
@@ -69,9 +69,9 @@ class HasOnlyReadOnly {
   // maps a json object with a list of HasOnlyReadOnly-objects as value to a dart map
   static Map<String, List<HasOnlyReadOnly>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<HasOnlyReadOnly>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = HasOnlyReadOnly.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = HasOnlyReadOnly.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/health_check_result.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/health_check_result.dart
index 1ea8db9305c..06a044bb153 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/health_check_result.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/health_check_result.dart
@@ -47,12 +47,12 @@ class HealthCheckResult {
   static List<HealthCheckResult> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <HealthCheckResult>[]
-      : json.map((v) => HealthCheckResult.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => HealthCheckResult.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, HealthCheckResult> mapFromJson(Map<String, dynamic> json) {
     final map = <String, HealthCheckResult>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = HealthCheckResult.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = HealthCheckResult.fromJson(value));
     }
     return map;
   }
@@ -60,9 +60,9 @@ class HealthCheckResult {
   // maps a json object with a list of HealthCheckResult-objects as value to a dart map
   static Map<String, List<HealthCheckResult>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<HealthCheckResult>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = HealthCheckResult.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = HealthCheckResult.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/inline_response_default.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/inline_response_default.dart
index c48b5c28e70..1cdee99a2de 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/inline_response_default.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/inline_response_default.dart
@@ -47,12 +47,12 @@ class InlineResponseDefault {
   static List<InlineResponseDefault> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <InlineResponseDefault>[]
-      : json.map((v) => InlineResponseDefault.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => InlineResponseDefault.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, InlineResponseDefault> mapFromJson(Map<String, dynamic> json) {
     final map = <String, InlineResponseDefault>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = InlineResponseDefault.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = InlineResponseDefault.fromJson(value));
     }
     return map;
   }
@@ -60,9 +60,9 @@ class InlineResponseDefault {
   // maps a json object with a list of InlineResponseDefault-objects as value to a dart map
   static Map<String, List<InlineResponseDefault>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<InlineResponseDefault>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = InlineResponseDefault.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = InlineResponseDefault.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/map_test.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/map_test.dart
index 9843c474910..23a54bd34ae 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/map_test.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/map_test.dart
@@ -67,7 +67,7 @@ class MapTest {
     : MapTest(
         mapMapOfString: json[r'map_map_of_string'] == null
           ? null
-          : Map.mapFromJson(json[r'map_map_of_string']),
+          : (json[r'map_map_of_string'] as Map).cast<String, Map>(),
         mapOfEnumString: json[r'map_of_enum_string'] == null ?
           null :
           (json[r'map_of_enum_string'] as Map).cast<String, String>(),
@@ -82,12 +82,12 @@ class MapTest {
   static List<MapTest> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <MapTest>[]
-      : json.map((v) => MapTest.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => MapTest.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, MapTest> mapFromJson(Map<String, dynamic> json) {
     final map = <String, MapTest>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = MapTest.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = MapTest.fromJson(value));
     }
     return map;
   }
@@ -95,9 +95,9 @@ class MapTest {
   // maps a json object with a list of MapTest-objects as value to a dart map
   static Map<String, List<MapTest>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<MapTest>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = MapTest.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = MapTest.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/mixed_properties_and_additional_properties_class.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/mixed_properties_and_additional_properties_class.dart
index b9a202de856..053427aafd1 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/mixed_properties_and_additional_properties_class.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/mixed_properties_and_additional_properties_class.dart
@@ -61,20 +61,18 @@ class MixedPropertiesAndAdditionalPropertiesClass {
         dateTime: json[r'dateTime'] == null
           ? null
           : DateTime.parse(json[r'dateTime']),
-        map: json[r'map'] == null
-          ? null
-          : Animal.mapFromJson(json[r'map']),
+            map: json[r'map']
     );
 
   static List<MixedPropertiesAndAdditionalPropertiesClass> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <MixedPropertiesAndAdditionalPropertiesClass>[]
-      : json.map((v) => MixedPropertiesAndAdditionalPropertiesClass.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => MixedPropertiesAndAdditionalPropertiesClass.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, MixedPropertiesAndAdditionalPropertiesClass> mapFromJson(Map<String, dynamic> json) {
     final map = <String, MixedPropertiesAndAdditionalPropertiesClass>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = MixedPropertiesAndAdditionalPropertiesClass.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = MixedPropertiesAndAdditionalPropertiesClass.fromJson(value));
     }
     return map;
   }
@@ -82,9 +80,9 @@ class MixedPropertiesAndAdditionalPropertiesClass {
   // maps a json object with a list of MixedPropertiesAndAdditionalPropertiesClass-objects as value to a dart map
   static Map<String, List<MixedPropertiesAndAdditionalPropertiesClass>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<MixedPropertiesAndAdditionalPropertiesClass>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = MixedPropertiesAndAdditionalPropertiesClass.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = MixedPropertiesAndAdditionalPropertiesClass.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model200_response.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model200_response.dart
index 15ecf90f50a..169581175eb 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model200_response.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model200_response.dart
@@ -56,12 +56,12 @@ class Model200Response {
   static List<Model200Response> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Model200Response>[]
-      : json.map((v) => Model200Response.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Model200Response.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Model200Response> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Model200Response>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Model200Response.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Model200Response.fromJson(value));
     }
     return map;
   }
@@ -69,9 +69,9 @@ class Model200Response {
   // maps a json object with a list of Model200Response-objects as value to a dart map
   static Map<String, List<Model200Response>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Model200Response>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Model200Response.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Model200Response.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_client.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_client.dart
index 08b98859176..039517160be 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_client.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_client.dart
@@ -47,12 +47,12 @@ class ModelClient {
   static List<ModelClient> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <ModelClient>[]
-      : json.map((v) => ModelClient.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => ModelClient.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, ModelClient> mapFromJson(Map<String, dynamic> json) {
     final map = <String, ModelClient>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = ModelClient.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = ModelClient.fromJson(value));
     }
     return map;
   }
@@ -60,9 +60,9 @@ class ModelClient {
   // maps a json object with a list of ModelClient-objects as value to a dart map
   static Map<String, List<ModelClient>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<ModelClient>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = ModelClient.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = ModelClient.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_file.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_file.dart
index 0ca3001c062..251cb11748b 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_file.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_file.dart
@@ -48,12 +48,12 @@ class ModelFile {
   static List<ModelFile> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <ModelFile>[]
-      : json.map((v) => ModelFile.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => ModelFile.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, ModelFile> mapFromJson(Map<String, dynamic> json) {
     final map = <String, ModelFile>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = ModelFile.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = ModelFile.fromJson(value));
     }
     return map;
   }
@@ -61,9 +61,9 @@ class ModelFile {
   // maps a json object with a list of ModelFile-objects as value to a dart map
   static Map<String, List<ModelFile>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<ModelFile>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = ModelFile.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = ModelFile.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_list.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_list.dart
index 973198375ad..c269cec60cf 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_list.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_list.dart
@@ -47,12 +47,12 @@ class ModelList {
   static List<ModelList> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <ModelList>[]
-      : json.map((v) => ModelList.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => ModelList.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, ModelList> mapFromJson(Map<String, dynamic> json) {
     final map = <String, ModelList>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = ModelList.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = ModelList.fromJson(value));
     }
     return map;
   }
@@ -60,9 +60,9 @@ class ModelList {
   // maps a json object with a list of ModelList-objects as value to a dart map
   static Map<String, List<ModelList>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<ModelList>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = ModelList.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = ModelList.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_return.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_return.dart
index 50c58ca70f1..b4a37d9f633 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_return.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/model_return.dart
@@ -47,12 +47,12 @@ class ModelReturn {
   static List<ModelReturn> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <ModelReturn>[]
-      : json.map((v) => ModelReturn.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => ModelReturn.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, ModelReturn> mapFromJson(Map<String, dynamic> json) {
     final map = <String, ModelReturn>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = ModelReturn.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = ModelReturn.fromJson(value));
     }
     return map;
   }
@@ -60,9 +60,9 @@ class ModelReturn {
   // maps a json object with a list of ModelReturn-objects as value to a dart map
   static Map<String, List<ModelReturn>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<ModelReturn>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = ModelReturn.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = ModelReturn.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/name.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/name.dart
index 264c1a8c04d..9068f61d639 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/name.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/name.dart
@@ -72,12 +72,12 @@ class Name {
   static List<Name> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Name>[]
-      : json.map((v) => Name.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Name.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Name> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Name>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Name.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Name.fromJson(value));
     }
     return map;
   }
@@ -85,9 +85,9 @@ class Name {
   // maps a json object with a list of Name-objects as value to a dart map
   static Map<String, List<Name>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Name>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Name.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Name.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/nullable_class.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/nullable_class.dart
index 0295e97b0d2..f1df88a935a 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/nullable_class.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/nullable_class.dart
@@ -144,26 +144,20 @@ class NullableClass {
         arrayNullableProp: Object.listFromJson(json[r'array_nullable_prop']),
         arrayAndItemsNullableProp: Object.listFromJson(json[r'array_and_items_nullable_prop']),
         arrayItemsNullable: Object.listFromJson(json[r'array_items_nullable']),
-        objectNullableProp: json[r'object_nullable_prop'] == null
-          ? null
-          : Object.mapFromJson(json[r'object_nullable_prop']),
-        objectAndItemsNullableProp: json[r'object_and_items_nullable_prop'] == null
-          ? null
-          : Object.mapFromJson(json[r'object_and_items_nullable_prop']),
-        objectItemsNullable: json[r'object_items_nullable'] == null
-          ? null
-          : Object.mapFromJson(json[r'object_items_nullable']),
+            objectNullableProp: json[r'object_nullable_prop']
+            objectAndItemsNullableProp: json[r'object_and_items_nullable_prop']
+            objectItemsNullable: json[r'object_items_nullable']
     );
 
   static List<NullableClass> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <NullableClass>[]
-      : json.map((v) => NullableClass.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => NullableClass.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, NullableClass> mapFromJson(Map<String, dynamic> json) {
     final map = <String, NullableClass>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = NullableClass.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = NullableClass.fromJson(value));
     }
     return map;
   }
@@ -171,9 +165,9 @@ class NullableClass {
   // maps a json object with a list of NullableClass-objects as value to a dart map
   static Map<String, List<NullableClass>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<NullableClass>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = NullableClass.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = NullableClass.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/number_only.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/number_only.dart
index d710d3b50b2..16cc2514577 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/number_only.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/number_only.dart
@@ -49,12 +49,12 @@ class NumberOnly {
   static List<NumberOnly> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <NumberOnly>[]
-      : json.map((v) => NumberOnly.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => NumberOnly.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, NumberOnly> mapFromJson(Map<String, dynamic> json) {
     final map = <String, NumberOnly>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = NumberOnly.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = NumberOnly.fromJson(value));
     }
     return map;
   }
@@ -62,9 +62,9 @@ class NumberOnly {
   // maps a json object with a list of NumberOnly-objects as value to a dart map
   static Map<String, List<NumberOnly>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<NumberOnly>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = NumberOnly.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = NumberOnly.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/order.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/order.dart
index a7b01582664..4cf8b636f47 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/order.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/order.dart
@@ -95,12 +95,12 @@ class Order {
   static List<Order> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Order>[]
-      : json.map((v) => Order.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Order.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Order> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Order>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Order.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Order.fromJson(value));
     }
     return map;
   }
@@ -108,9 +108,9 @@ class Order {
   // maps a json object with a list of Order-objects as value to a dart map
   static Map<String, List<Order>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Order>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Order.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Order.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_composite.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_composite.dart
index d2942660d23..c7aeb68f1ae 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_composite.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_composite.dart
@@ -67,12 +67,12 @@ class OuterComposite {
   static List<OuterComposite> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <OuterComposite>[]
-      : json.map((v) => OuterComposite.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => OuterComposite.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, OuterComposite> mapFromJson(Map<String, dynamic> json) {
     final map = <String, OuterComposite>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = OuterComposite.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = OuterComposite.fromJson(value));
     }
     return map;
   }
@@ -80,9 +80,9 @@ class OuterComposite {
   // maps a json object with a list of OuterComposite-objects as value to a dart map
   static Map<String, List<OuterComposite>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<OuterComposite>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = OuterComposite.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = OuterComposite.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_object_with_enum_property.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_object_with_enum_property.dart
index 4d58d276284..accf401ed9a 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_object_with_enum_property.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_object_with_enum_property.dart
@@ -45,12 +45,12 @@ class OuterObjectWithEnumProperty {
   static List<OuterObjectWithEnumProperty> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <OuterObjectWithEnumProperty>[]
-      : json.map((v) => OuterObjectWithEnumProperty.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => OuterObjectWithEnumProperty.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, OuterObjectWithEnumProperty> mapFromJson(Map<String, dynamic> json) {
     final map = <String, OuterObjectWithEnumProperty>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = OuterObjectWithEnumProperty.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = OuterObjectWithEnumProperty.fromJson(value));
     }
     return map;
   }
@@ -58,9 +58,9 @@ class OuterObjectWithEnumProperty {
   // maps a json object with a list of OuterObjectWithEnumProperty-objects as value to a dart map
   static Map<String, List<OuterObjectWithEnumProperty>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<OuterObjectWithEnumProperty>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = OuterObjectWithEnumProperty.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = OuterObjectWithEnumProperty.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/pet.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/pet.dart
index 47ef86dfcb2..3043edb921f 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/pet.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/pet.dart
@@ -91,12 +91,12 @@ class Pet {
   static List<Pet> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Pet>[]
-      : json.map((v) => Pet.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Pet.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Pet> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Pet>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Pet.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Pet.fromJson(value));
     }
     return map;
   }
@@ -104,9 +104,9 @@ class Pet {
   // maps a json object with a list of Pet-objects as value to a dart map
   static Map<String, List<Pet>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Pet>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Pet.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Pet.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/read_only_first.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/read_only_first.dart
index 3d8382c019e..b0eb02b6942 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/read_only_first.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/read_only_first.dart
@@ -56,12 +56,12 @@ class ReadOnlyFirst {
   static List<ReadOnlyFirst> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <ReadOnlyFirst>[]
-      : json.map((v) => ReadOnlyFirst.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => ReadOnlyFirst.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, ReadOnlyFirst> mapFromJson(Map<String, dynamic> json) {
     final map = <String, ReadOnlyFirst>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = ReadOnlyFirst.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = ReadOnlyFirst.fromJson(value));
     }
     return map;
   }
@@ -69,9 +69,9 @@ class ReadOnlyFirst {
   // maps a json object with a list of ReadOnlyFirst-objects as value to a dart map
   static Map<String, List<ReadOnlyFirst>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<ReadOnlyFirst>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = ReadOnlyFirst.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = ReadOnlyFirst.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/special_model_name.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/special_model_name.dart
index 846ca82a7db..e43a6b267d2 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/special_model_name.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/special_model_name.dart
@@ -47,12 +47,12 @@ class SpecialModelName {
   static List<SpecialModelName> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <SpecialModelName>[]
-      : json.map((v) => SpecialModelName.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => SpecialModelName.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, SpecialModelName> mapFromJson(Map<String, dynamic> json) {
     final map = <String, SpecialModelName>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = SpecialModelName.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = SpecialModelName.fromJson(value));
     }
     return map;
   }
@@ -60,9 +60,9 @@ class SpecialModelName {
   // maps a json object with a list of SpecialModelName-objects as value to a dart map
   static Map<String, List<SpecialModelName>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<SpecialModelName>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = SpecialModelName.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = SpecialModelName.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/tag.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/tag.dart
index 63132f08a3a..0cd372910b9 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/tag.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/tag.dart
@@ -56,12 +56,12 @@ class Tag {
   static List<Tag> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <Tag>[]
-      : json.map((v) => Tag.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => Tag.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, Tag> mapFromJson(Map<String, dynamic> json) {
     final map = <String, Tag>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = Tag.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = Tag.fromJson(value));
     }
     return map;
   }
@@ -69,9 +69,9 @@ class Tag {
   // maps a json object with a list of Tag-objects as value to a dart map
   static Map<String, List<Tag>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<Tag>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = Tag.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = Tag.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/user.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/user.dart
index bb512af491f..0eb3716fceb 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/user.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/user.dart
@@ -111,12 +111,12 @@ class User {
   static List<User> listFromJson(List<dynamic> json, {bool emptyIsNull, bool growable,}) =>
     json == null || json.isEmpty
       ? true == emptyIsNull ? null : <User>[]
-      : json.map((v) => User.fromJson(v)).toList(growable: true == growable);
+      : json.map((dynamic value) => User.fromJson(value)).toList(growable: true == growable);
 
   static Map<String, User> mapFromJson(Map<String, dynamic> json) {
     final map = <String, User>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) => map[key] = User.fromJson(v));
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) => map[key] = User.fromJson(value));
     }
     return map;
   }
@@ -124,9 +124,9 @@ class User {
   // maps a json object with a list of User-objects as value to a dart map
   static Map<String, List<User>> mapListFromJson(Map<String, dynamic> json, {bool emptyIsNull, bool growable,}) {
     final map = <String, List<User>>{};
-    if (json != null && json.isNotEmpty) {
-      json.forEach((String key, dynamic v) {
-        map[key] = User.listFromJson(v, emptyIsNull: emptyIsNull, growable: growable);
+    if (json?.isNotEmpty == true) {
+      json.forEach((key, value) {
+        map[key] = User.listFromJson(value, emptyIsNull: emptyIsNull, growable: growable,);
       });
     }
     return map;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_json_serializable_client_lib_fake/.openapi-generator/FILES b/samples/openapi3/client/petstore/dart2/petstore_json_serializable_client_lib_fake/.openapi-generator/FILES
index a9cd914811b..56e6b6ec96e 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_json_serializable_client_lib_fake/.openapi-generator/FILES
+++ b/samples/openapi3/client/petstore/dart2/petstore_json_serializable_client_lib_fake/.openapi-generator/FILES
@@ -1,6 +1,7 @@
 .gitignore
 .travis.yml
 README.md
+analysis_options.yaml
 build.yaml
 doc/AdditionalPropertiesClass.md
 doc/Animal.md
diff --git a/samples/openapi3/client/petstore/dart2/petstore_json_serializable_client_lib_fake/analysis_options.yaml b/samples/openapi3/client/petstore/dart2/petstore_json_serializable_client_lib_fake/analysis_options.yaml
new file mode 100644
index 00000000000..83d5a10bd7b
--- /dev/null
+++ b/samples/openapi3/client/petstore/dart2/petstore_json_serializable_client_lib_fake/analysis_options.yaml
@@ -0,0 +1,3 @@
+analyzer:
+  strong-mode:
+    implicit-casts: true
diff --git a/samples/openapi3/client/petstore/dart2/petstore_json_serializable_client_lib_fake/lib/api_client.dart b/samples/openapi3/client/petstore/dart2/petstore_json_serializable_client_lib_fake/lib/api_client.dart
index 65c9ec57844..02f98fe17a4 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_json_serializable_client_lib_fake/lib/api_client.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_json_serializable_client_lib_fake/lib/api_client.dart
@@ -61,7 +61,7 @@ class ApiClient {
   Future<Response> invokeAPI(
     String path,
     String method,
-    Iterable<QueryParam> queryParams,
+    List<QueryParam> queryParams,
     Object body,
     Map<String, String> headerParams,
     Map<String, String> formParams,
@@ -156,13 +156,13 @@ class ApiClient {
     List<QueryParam> queryParams,
     Map<String, String> headerParams,
   ) {
-    authNames.forEach((authName) {
+    for(final authName in authNames) {
       final auth = _authentications[authName];
       if (auth == null) {
         throw ArgumentError('Authentication undefined: $authName');
       }
       auth.applyToParams(queryParams, headerParams);
-    });
+    }
   }
 
 }