diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3359467f..4617c87e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+# 2.12.1
+* Fixed return type nullability ([#670](https://github.com/epam-cross-platform-lab/swagger-dart-code-generator/issues/670))
+* Fixed generation of DateTime return types
+
+# 2.11.13
+
+* Fixed different issues
+
 # 2.11.12
 
 * Added generation of const constructors
diff --git a/lib/src/code_generators/swagger_additions_generator.dart b/lib/src/code_generators/swagger_additions_generator.dart
index a14e25da..6b3cab31 100644
--- a/lib/src/code_generators/swagger_additions_generator.dart
+++ b/lib/src/code_generators/swagger_additions_generator.dart
@@ -198,10 +198,16 @@ class \$JsonSerializableConverter extends chopper.JsonConverter {
       return chopper.Response(response.base, null, error: response.error);
     }
 
-    if(ResultType == String) {
+    if (ResultType == String) {
       return response.copyWith();
     }
 
+    if (ResultType == DateTime) {
+      return response.copyWith(
+          body: DateTime.parse((response.body as String).replaceAll('"', ''))
+              as ResultType);
+    }
+
     final jsonRes = await super.convertResponse(response);
     return jsonRes.copyWith<ResultType>(
         body: \$jsonDecoder.decode<Item>(jsonRes.body) as ResultType);
diff --git a/lib/src/code_generators/swagger_models_generator.dart b/lib/src/code_generators/swagger_models_generator.dart
index 431bdcac..9fedf0b3 100644
--- a/lib/src/code_generators/swagger_models_generator.dart
+++ b/lib/src/code_generators/swagger_models_generator.dart
@@ -443,7 +443,13 @@ abstract class SwaggerModelsGenerator extends SwaggerGeneratorBase {
 
     final includeIfNullString = generateIncludeIfNullString();
 
-    if (typeName != kDynamic && (prop.isNullable || options.nullableFields)) {
+    if (typeName != kDynamic &&
+        (prop.isNullable || options.nullableModels.contains(typeName))) {
+      typeName = typeName.makeNullable();
+    }
+
+    if (requiredProperties.isNotEmpty &&
+        !requiredProperties.contains(propertyKey)) {
       typeName = typeName.makeNullable();
     }
 
@@ -564,15 +570,11 @@ static $returnType $fromJsonFunction($valueType? value) => $enumNameCamelCase$fr
     String propertyKey,
     SwaggerSchema prop,
   ) {
-    if (options.nullableModels.contains(className) || prop.isNullable == true) {
-      return true;
-    }
-
     if (requiredProperties.contains(propertyKey)) {
       return false;
     }
 
-    return options.nullableFields;
+    return options.nullableModels.contains(className) || prop.isNullable;
   }
 
   String nullable(
@@ -639,11 +641,7 @@ static $returnType $fromJsonFunction($valueType? value) => $enumNameCamelCase$fr
     final jsonKeyContent =
         "@JsonKey(name: '${_validatePropertyKey(propertyKey)}'$includeIfNullString${unknownEnumValue.jsonKey}$dateToJsonValue)\n";
 
-    if (prop.isNullable || options.nullableFields) {
-      typeName = typeName.makeNullable();
-    }
-
-    if (requiredProperties.isNotEmpty &&
+    if ((prop.isNullable || options.nullableModels.contains(className)) &&
         !requiredProperties.contains(propertyKey)) {
       typeName = typeName.makeNullable();
     }
@@ -708,11 +706,7 @@ static $returnType $fromJsonFunction($valueType? value) => $enumNameCamelCase$fr
     final jsonKeyContent =
         "@JsonKey(name: '${_validatePropertyKey(propertyKey)}'$includeIfNullString${unknownEnumValue.jsonKey})\n";
 
-    if (prop.isNullable || options.nullableFields) {
-      typeName = typeName.makeNullable();
-    }
-
-    if (requiredProperties.isNotEmpty &&
+    if ((prop.isNullable || options.nullableModels.contains(className)) &&
         !requiredProperties.contains(propertyKey)) {
       typeName = typeName.makeNullable();
     }
@@ -758,7 +752,8 @@ static $returnType $fromJsonFunction($valueType? value) => $enumNameCamelCase$fr
       typeName += options.modelPostfix;
     }
 
-    final isPropertyNullable = refSchema?.isNullable == true ||
+    final isPropertyNullable = options.nullableModels.contains(className) ||
+        refSchema?.isNullable == true ||
         isNullable(className, requiredProperties, propertyKey, prop);
 
     final unknownEnumValue = generateEnumValue(
@@ -781,18 +776,16 @@ static $returnType $fromJsonFunction($valueType? value) => $enumNameCamelCase$fr
     final jsonKeyContent =
         "@JsonKey(name: '${_validatePropertyKey(propertyKey)}'$includeIfNullString${unknownEnumValue.jsonKey})\n";
 
-    if (prop.isNullable || options.nullableFields) {
-      typeName = typeName.makeNullable();
-    }
-
-    if (requiredProperties.isNotEmpty &&
+    if ((prop.isNullable || options.nullableModels.contains(className)) &&
         !requiredProperties.contains(propertyKey)) {
       typeName = typeName.makeNullable();
     }
 
     final propertySchema = allClasses[prop.ref.getUnformattedRef()];
 
-    if (propertySchema?.isNullable == true || isPropertyNullable) {
+    if (propertySchema?.isNullable == true ||
+        isPropertyNullable ||
+        options.nullableModels.contains(className)) {
       typeName = typeName.makeNullable();
     }
 
@@ -832,11 +825,7 @@ static $returnType $fromJsonFunction($valueType? value) => $enumNameCamelCase$fr
 
     var enumPropertyName = className.capitalize + key.capitalize;
 
-    if (prop.isNullable || options.nullableFields) {
-      enumPropertyName = enumPropertyName.makeNullable();
-    }
-
-    if (requiredProperties.isNotEmpty &&
+    if ((prop.isNullable || options.nullableModels.contains(className)) &&
         !requiredProperties.contains(propertyKey)) {
       enumPropertyName = enumPropertyName.makeNullable();
     }
@@ -986,11 +975,7 @@ static $returnType $fromJsonFunction($valueType? value) => $enumNameCamelCase$fr
 
     var listPropertyName = 'List<$typeName>';
 
-    if (prop.isNullable || options.nullableFields) {
-      listPropertyName = listPropertyName.makeNullable();
-    }
-
-    if (requiredProperties.isNotEmpty &&
+    if ((prop.isNullable || options.nullableModels.contains(className)) &&
         !requiredProperties.contains(propertyKey)) {
       listPropertyName = listPropertyName.makeNullable();
     }
@@ -1041,6 +1026,7 @@ static $returnType $fromJsonFunction($valueType? value) => $enumNameCamelCase$fr
       defaultValue: prop.defaultValue,
       isList: false,
       isNullable: isNullable(className, requiredProperties, propertyKey, prop),
+      className: className,
     );
 
     final dateToJsonValue = generateToJsonForDate(prop);
@@ -1061,11 +1047,7 @@ static $returnType $fromJsonFunction($valueType? value) => $enumNameCamelCase$fr
       jsonKeyContent += ')\n';
     }
 
-    if (prop.isNullable || options.nullableFields) {
-      typeName = typeName.makeNullable();
-    }
-
-    if (requiredProperties.isNotEmpty &&
+    if ((prop.isNullable || options.nullableModels.contains(className)) &&
         !requiredProperties.contains(propertyKey)) {
       typeName = typeName.makeNullable();
     }
@@ -1325,9 +1307,8 @@ static $returnType $fromJsonFunction($valueType? value) => $enumNameCamelCase$fr
 
       propertyNames.add(fieldName);
 
-      final isNullableProperty = options.nullableModels.contains(className) ||
-          options.nullableFields ||
-          value.isNullable;
+      final isNullableProperty =
+          options.nullableModels.contains(className) || value.isNullable;
 
       final isRequiredProperty = requiredProperties.contains(key);
 
diff --git a/lib/src/code_generators/swagger_requests_generator.dart b/lib/src/code_generators/swagger_requests_generator.dart
index 5a4cc87f..2abab3eb 100644
--- a/lib/src/code_generators/swagger_requests_generator.dart
+++ b/lib/src/code_generators/swagger_requests_generator.dart
@@ -448,8 +448,9 @@ class SwaggerRequestsGenerator extends SwaggerGeneratorBase {
     var allModelsString = '';
 
     allModels.toSet().forEach((model) {
+      final validatedName = getValidatedClassName(model);
       allModelsString +=
-          'generatedMapping.putIfAbsent($model, () => $model.fromJsonFactory);\n';
+          'generatedMapping.putIfAbsent($validatedName, () => $validatedName.fromJsonFactory);\n';
     });
 
     return Code(
diff --git a/lib/src/models/generator_options.dart b/lib/src/models/generator_options.dart
index f4c3ca24..4be5e95f 100644
--- a/lib/src/models/generator_options.dart
+++ b/lib/src/models/generator_options.dart
@@ -37,7 +37,6 @@ class GeneratorOptions {
     this.overridenModels = const [],
     this.generateToJsonFor = const [],
     this.multipartFileType = 'List<int>',
-    this.nullableFields = true,
   });
 
   /// Build options from a JSON map.
@@ -50,9 +49,6 @@ class GeneratorOptions {
   @JsonKey(defaultValue: true)
   final bool withBaseUrl;
 
-  @JsonKey(defaultValue: true)
-  final bool nullableFields;
-
   @JsonKey(defaultValue: false)
   final bool addBasePathToRequests;
 
diff --git a/lib/src/models/generator_options.g2.dart b/lib/src/models/generator_options.g2.dart
index 97a95dca..6050b4a8 100644
--- a/lib/src/models/generator_options.g2.dart
+++ b/lib/src/models/generator_options.g2.dart
@@ -84,14 +84,12 @@ GeneratorOptions _$GeneratorOptionsFromJson(Map json) => GeneratorOptions(
               .toList() ??
           [],
       multipartFileType: json['multipart_file_type'] as String? ?? 'List<int>',
-      nullableFields: json['nullable_fields'] as bool? ?? true,
     );
 
 Map<String, dynamic> _$GeneratorOptionsToJson(GeneratorOptions instance) =>
     <String, dynamic>{
       'use_path_for_request_names': instance.usePathForRequestNames,
       'with_base_url': instance.withBaseUrl,
-      'nullable_fields': instance.nullableFields,
       'add_base_path_to_requests': instance.addBasePathToRequests,
       'page_width': instance.pageWidth,
       'override_to_string': instance.overrideToString,
diff --git a/lib/src/swagger_models/responses/swagger_schema.dart b/lib/src/swagger_models/responses/swagger_schema.dart
index 579b8ad8..a33d1121 100644
--- a/lib/src/swagger_models/responses/swagger_schema.dart
+++ b/lib/src/swagger_models/responses/swagger_schema.dart
@@ -21,7 +21,7 @@ class SwaggerSchema {
     this.required = const [],
     this.description = '',
     this.enumNames,
-    this.isNullable = false,
+    this.isNullable = true,
     this.hasAdditionalProperties = false,
     this.msEnum,
   });
@@ -76,7 +76,7 @@ class SwaggerSchema {
   @JsonKey(name: 'properties', defaultValue: {})
   Map<String, SwaggerSchema> properties;
 
-  @JsonKey(name: 'nullable', defaultValue: false)
+  @JsonKey(name: 'nullable', defaultValue: true)
   bool isNullable;
 
   @JsonKey(name: 'schema')
diff --git a/lib/src/swagger_models/responses/swagger_schema.g2.dart b/lib/src/swagger_models/responses/swagger_schema.g2.dart
index 73e1998d..af44df10 100644
--- a/lib/src/swagger_models/responses/swagger_schema.g2.dart
+++ b/lib/src/swagger_models/responses/swagger_schema.g2.dart
@@ -44,7 +44,7 @@ SwaggerSchema _$SwaggerSchemaFromJson(Map<String, dynamic> json) =>
       enumNames: (json['enumNames'] as List<dynamic>?)
           ?.map((e) => e as String)
           .toList(),
-      isNullable: json['nullable'] as bool? ?? false,
+      isNullable: json['nullable'] as bool? ?? true,
       hasAdditionalProperties: json['additionalProperties'] == null
           ? false
           : _additionalsFromJson(json['additionalProperties']),
diff --git a/pubspec.yaml b/pubspec.yaml
index a620aa67..ff33efd3 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,6 +1,6 @@
 name: swagger_dart_code_generator
 
-version: 2.11.12
+version: 2.12.1
 
 homepage: https://github.com/epam-cross-platform-lab/swagger-dart-code-generator
 repository: https://github.com/epam-cross-platform-lab/swagger-dart-code-generator
diff --git a/test/generator_tests/models_generator_test.dart b/test/generator_tests/models_generator_test.dart
index 496c7457..ef53e563 100644
--- a/test/generator_tests/models_generator_test.dart
+++ b/test/generator_tests/models_generator_test.dart
@@ -12,14 +12,12 @@ void main() {
     GeneratorOptions(
       inputFolder: '',
       outputFolder: '',
-      nullableFields: false,
     ),
   );
   final generator2 = SwaggerModelsGeneratorV2(
     GeneratorOptions(
       inputFolder: '',
       outputFolder: '',
-      nullableFields: false,
     ),
   );
 
@@ -292,7 +290,7 @@ void main() {
       const className = 'Animals';
       const propertyKey = 'Dog';
       const jsonKeyExpectedResult = "\t@JsonKey(name: 'Dog')\n";
-      const fieldExpectedResult = '\tfinal Pet dog';
+      const fieldExpectedResult = '\tfinal Pet? dog';
       final result = generator.generatePropertyContentBySchema(
         map,
         propertyName,
@@ -317,7 +315,7 @@ void main() {
 
       const className = 'Animals';
       const jsonKeyExpectedResult = "\t@JsonKey(name: 'Animals')\n";
-      const fieldExpectedResult = 'final Pet animals';
+      const fieldExpectedResult = 'final Pet? animals';
       final result = generator.generatePropertiesContent(
         SwaggerRoot.empty,
         map,
@@ -344,7 +342,7 @@ void main() {
 
       const className = 'Animals';
       const jsonKeyExpectedResult = "\t@JsonKey(name: 'Animals')\n";
-      const fieldExpectedResult = 'final Pet animals';
+      const fieldExpectedResult = 'final Pet? animals';
       final result = generator.generatePropertiesContent(
         SwaggerRoot.empty,
         map,
@@ -369,7 +367,7 @@ void main() {
 
       const className = 'Animals';
       const jsonKeyExpectedResult = "\t@JsonKey(name: 'animals')\n";
-      const fieldExpectedResult = 'final Pet animals';
+      const fieldExpectedResult = 'final Pet? animals';
       final result = generator.generatePropertiesContent(
         SwaggerRoot.empty,
         map,
@@ -394,7 +392,7 @@ void main() {
 
       const className = 'Animals';
       const jsonKeyExpectedResult = "\t@JsonKey(name: '\\\$with')\n";
-      const fieldExpectedResult = 'final Pet \$with';
+      const fieldExpectedResult = 'final Pet? \$with';
       final result = generator.generatePropertiesContent(
         SwaggerRoot.empty,
         map,
@@ -422,7 +420,7 @@ void main() {
       const jsonKeyExpectedResult =
           "@JsonKey(name: 'Dog', defaultValue: <Object>[])";
 
-      const propertyExpectedResult = 'final List<Object> dog';
+      const propertyExpectedResult = 'final List<Object>? dog';
       final result = generator.generateListPropertyContent(
         propertyName,
         propertyKey,
@@ -482,7 +480,7 @@ void main() {
         {},
       );
 
-      expect(result, contains('final List<TestOriginalRef> dog;'));
+      expect(result, contains('final List<TestOriginalRef>? dog;'));
     });
 
     test('Should return List<Object> by ref', () {
@@ -505,7 +503,7 @@ void main() {
         {},
       );
 
-      expect(result, contains('final List<TestObject> dog;'));
+      expect(result, contains('final List<TestObject>? dog;'));
     });
   });