diff --git a/modules/openapi-generator/src/main/resources/dart-dio/api.mustache b/modules/openapi-generator/src/main/resources/dart-dio/api.mustache
index 3ecff3ef146..dcfedc065ed 100644
--- a/modules/openapi-generator/src/main/resources/dart-dio/api.mustache
+++ b/modules/openapi-generator/src/main/resources/dart-dio/api.mustache
@@ -33,7 +33,8 @@ class {{classname}} {
         final String _path = '{{{path}}}'{{#pathParams}}.replaceAll('{' r'{{baseName}}' '}', {{{paramName}}}.toString()){{/pathParams}};
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ {{#httpUserAgent}}
+            'User-Agent': '{{{.}}}',{{/httpUserAgent}}
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/modules/openapi-generator/src/main/resources/dart/api_client.mustache b/modules/openapi-generator/src/main/resources/dart/api_client.mustache
index 0e240523542..9bb3d59bc52 100644
--- a/modules/openapi-generator/src/main/resources/dart/api_client.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/api_client.mustache
@@ -23,6 +23,7 @@ class ApiClient {
     _authentications['{{name}}'] = new HttpBasicAuth();{{/isBasic}}{{#isApiKey}}
     _authentications['{{name}}'] = new ApiKeyAuth({{#isKeyInHeader}}"header"{{/isKeyInHeader}}{{^isKeyInHeader}}"query"{{/isKeyInHeader}}, "{{keyParamName}}");{{/isApiKey}}{{#isOAuth}}
     _authentications['{{name}}'] = new OAuth();{{/isOAuth}}{{/authMethods}}
+    {{#httpUserAgent}}addDefaultHeader('User-Agent', '{{{.}}}');{{/httpUserAgent}}
   }
 
   void addDefaultHeader(String key, String value) {
diff --git a/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/pet_api.dart b/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/pet_api.dart
index 795b627fb40..fe5c9299841 100644
--- a/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/pet_api.dart
+++ b/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/pet_api.dart
@@ -37,7 +37,7 @@ class PetApi {
         final String _path = '/pet';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -96,7 +96,7 @@ class PetApi {
         final String _path = '/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -147,7 +147,7 @@ class PetApi {
         final String _path = '/pet/findByStatus';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -217,7 +217,7 @@ class PetApi {
         final String _path = '/pet/findByTags';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -287,7 +287,7 @@ class PetApi {
         final String _path = '/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -355,7 +355,7 @@ class PetApi {
         final String _path = '/pet';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -415,7 +415,7 @@ class PetApi {
         final String _path = '/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -475,7 +475,7 @@ class PetApi {
         final String _path = '/pet/{petId}/uploadImage'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/store_api.dart b/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/store_api.dart
index ed20fd6fce5..f9a8754907a 100644
--- a/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/store_api.dart
+++ b/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/store_api.dart
@@ -34,7 +34,7 @@ class StoreApi {
         final String _path = '/store/order/{orderId}'.replaceAll('{' r'orderId' '}', orderId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -78,7 +78,7 @@ class StoreApi {
         final String _path = '/store/inventory';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -149,7 +149,7 @@ class StoreApi {
         final String _path = '/store/order/{orderId}'.replaceAll('{' r'orderId' '}', orderId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -210,7 +210,7 @@ class StoreApi {
         final String _path = '/store/order';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/user_api.dart b/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/user_api.dart
index fc504efe821..17b551bc911 100644
--- a/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/user_api.dart
+++ b/samples/client/petstore/dart-dio/petstore_client_lib/lib/api/user_api.dart
@@ -34,7 +34,7 @@ class UserApi {
         final String _path = '/user';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -84,7 +84,7 @@ class UserApi {
         final String _path = '/user/createWithArray';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -134,7 +134,7 @@ class UserApi {
         final String _path = '/user/createWithList';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -184,7 +184,7 @@ class UserApi {
         final String _path = '/user/{username}'.replaceAll('{' r'username' '}', username.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -229,7 +229,7 @@ class UserApi {
         final String _path = '/user/{username}'.replaceAll('{' r'username' '}', username.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -291,7 +291,7 @@ class UserApi {
         final String _path = '/user/login';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -349,7 +349,7 @@ class UserApi {
         final String _path = '/user/logout';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -395,7 +395,7 @@ class UserApi {
         final String _path = '/user/{username}'.replaceAll('{' r'username' '}', username.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/pet_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/pet_api.dart
index f91d7d0125a..95db7626674 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/pet_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/pet_api.dart
@@ -37,7 +37,7 @@ class PetApi {
         final String _path = '/pet';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -112,7 +112,7 @@ class PetApi {
         final String _path = '/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -163,7 +163,7 @@ class PetApi {
         final String _path = '/pet/findByStatus';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -233,7 +233,7 @@ class PetApi {
         final String _path = '/pet/findByTags';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -303,7 +303,7 @@ class PetApi {
         final String _path = '/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -371,7 +371,7 @@ class PetApi {
         final String _path = '/pet';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -447,7 +447,7 @@ class PetApi {
         final String _path = '/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -507,7 +507,7 @@ class PetApi {
         final String _path = '/pet/{petId}/uploadImage'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/store_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/store_api.dart
index ba3f241333e..5f58e788091 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/store_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/store_api.dart
@@ -34,7 +34,7 @@ class StoreApi {
         final String _path = '/store/order/{orderId}'.replaceAll('{' r'orderId' '}', orderId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -78,7 +78,7 @@ class StoreApi {
         final String _path = '/store/inventory';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -149,7 +149,7 @@ class StoreApi {
         final String _path = '/store/order/{orderId}'.replaceAll('{' r'orderId' '}', orderId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -210,7 +210,7 @@ class StoreApi {
         final String _path = '/store/order';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/user_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/user_api.dart
index cb890e1846c..a4d59b2978c 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/user_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/lib/api/user_api.dart
@@ -34,7 +34,7 @@ class UserApi {
         final String _path = '/user';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -93,7 +93,7 @@ class UserApi {
         final String _path = '/user/createWithArray';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -152,7 +152,7 @@ class UserApi {
         final String _path = '/user/createWithList';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -211,7 +211,7 @@ class UserApi {
         final String _path = '/user/{username}'.replaceAll('{' r'username' '}', username.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -263,7 +263,7 @@ class UserApi {
         final String _path = '/user/{username}'.replaceAll('{' r'username' '}', username.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -325,7 +325,7 @@ class UserApi {
         final String _path = '/user/login';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -383,7 +383,7 @@ class UserApi {
         final String _path = '/user/logout';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -436,7 +436,7 @@ class UserApi {
         final String _path = '/user/{username}'.replaceAll('{' r'username' '}', username.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/another_fake_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/another_fake_api.dart
index 16e34300387..72310ff3533 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/another_fake_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/another_fake_api.dart
@@ -33,7 +33,7 @@ class AnotherFakeApi {
         final String _path = '/another-fake/dummy';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/default_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/default_api.dart
index 1e93ce8718a..a47b383960b 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/default_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/default_api.dart
@@ -32,7 +32,7 @@ class DefaultApi {
         final String _path = '/foo';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/fake_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/fake_api.dart
index 95dd5da583d..96d776d36f9 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/fake_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/fake_api.dart
@@ -40,7 +40,7 @@ class FakeApi {
         final String _path = '/fake/health';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -103,7 +103,7 @@ class FakeApi {
         final String _path = '/fake/http-signature-test';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -163,7 +163,7 @@ class FakeApi {
         final String _path = '/fake/outer/boolean';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -226,7 +226,7 @@ class FakeApi {
         final String _path = '/fake/outer/composite';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -294,7 +294,7 @@ class FakeApi {
         final String _path = '/fake/outer/number';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -357,7 +357,7 @@ class FakeApi {
         final String _path = '/fake/outer/string';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -420,7 +420,7 @@ class FakeApi {
         final String _path = '/fake/body-with-file-schema';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -473,7 +473,7 @@ class FakeApi {
         final String _path = '/fake/body-with-query-params';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -526,7 +526,7 @@ class FakeApi {
         final String _path = '/fake';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -607,7 +607,7 @@ class FakeApi {
         final String _path = '/fake';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -684,7 +684,7 @@ class FakeApi {
         final String _path = '/fake';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -748,7 +748,7 @@ class FakeApi {
         final String _path = '/fake';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -804,7 +804,7 @@ class FakeApi {
         final String _path = '/fake/inline-additionalProperties';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -857,7 +857,7 @@ class FakeApi {
         final String _path = '/fake/jsonFormData';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -914,7 +914,7 @@ class FakeApi {
         final String _path = '/fake/test-query-paramters';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/fake_classname_tags123_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/fake_classname_tags123_api.dart
index 222097970a1..81d1c554818 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/fake_classname_tags123_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/fake_classname_tags123_api.dart
@@ -33,7 +33,7 @@ class FakeClassnameTags123Api {
         final String _path = '/fake_classname_test';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/pet_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/pet_api.dart
index 4572f3c2a0d..6bb8363f2ae 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/pet_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/pet_api.dart
@@ -37,7 +37,7 @@ class PetApi {
         final String _path = '/pet';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -96,7 +96,7 @@ class PetApi {
         final String _path = '/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -147,7 +147,7 @@ class PetApi {
         final String _path = '/pet/findByStatus';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -217,7 +217,7 @@ class PetApi {
         final String _path = '/pet/findByTags';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -287,7 +287,7 @@ class PetApi {
         final String _path = '/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -355,7 +355,7 @@ class PetApi {
         final String _path = '/pet';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -415,7 +415,7 @@ class PetApi {
         final String _path = '/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -475,7 +475,7 @@ class PetApi {
         final String _path = '/pet/{petId}/uploadImage'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -551,7 +551,7 @@ class PetApi {
         final String _path = '/fake/{petId}/uploadImageWithRequiredFile'.replaceAll('{' r'petId' '}', petId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/store_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/store_api.dart
index a1bea34d14f..b9be3d2f72d 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/store_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/store_api.dart
@@ -34,7 +34,7 @@ class StoreApi {
         final String _path = '/store/order/{order_id}'.replaceAll('{' r'order_id' '}', orderId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -78,7 +78,7 @@ class StoreApi {
         final String _path = '/store/inventory';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -149,7 +149,7 @@ class StoreApi {
         final String _path = '/store/order/{order_id}'.replaceAll('{' r'order_id' '}', orderId.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -210,7 +210,7 @@ class StoreApi {
         final String _path = '/store/order';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/user_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/user_api.dart
index 87dbb0b8d14..e73986ac493 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/user_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/api/user_api.dart
@@ -34,7 +34,7 @@ class UserApi {
         final String _path = '/user';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -86,7 +86,7 @@ class UserApi {
         final String _path = '/user/createWithArray';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -138,7 +138,7 @@ class UserApi {
         final String _path = '/user/createWithList';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -190,7 +190,7 @@ class UserApi {
         final String _path = '/user/{username}'.replaceAll('{' r'username' '}', username.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -235,7 +235,7 @@ class UserApi {
         final String _path = '/user/{username}'.replaceAll('{' r'username' '}', username.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -297,7 +297,7 @@ class UserApi {
         final String _path = '/user/login';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -355,7 +355,7 @@ class UserApi {
         final String _path = '/user/logout';
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;
@@ -401,7 +401,7 @@ class UserApi {
         final String _path = '/user/{username}'.replaceAll('{' r'username' '}', username.toString());
 
         final queryParams = <String, dynamic>{};
-        final headerParams = <String, dynamic>{
+        final headerParams = <String, dynamic>{ 
             if (headers != null) ...headers,
         };
         dynamic bodyData;