diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractDartCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractDartCodegen.java
index 6cd5d2926e8..c5d8f65516d 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractDartCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractDartCodegen.java
@@ -1,7 +1,6 @@
 package org.openapitools.codegen.languages;
 
 import com.google.common.collect.Lists;
-import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
 import io.swagger.v3.oas.models.Operation;
 import io.swagger.v3.oas.models.media.ArraySchema;
@@ -29,6 +28,9 @@ public abstract class AbstractDartCodegen extends DefaultCodegen {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(AbstractDartCodegen.class);
 
+    protected static final List<String> DEFAULT_SUPPORTED_CONTENT_TYPES = Arrays.asList(
+            "application/json", "application/x-www-form-urlencoded", "multipart/form-data");
+
     public static final String PUB_LIBRARY = "pubLibrary";
     public static final String PUB_NAME = "pubName";
     public static final String PUB_VERSION = "pubVersion";
@@ -556,6 +558,68 @@ public abstract class AbstractDartCodegen extends DefaultCodegen {
         return op;
     }
 
+    @Override
+    public Map<String, Object> postProcessOperationsWithModels(Map<String, Object> objs, List<Object> allModels) {
+        super.postProcessOperationsWithModels(objs, allModels);
+        Map<String, Object> operations = (Map<String, Object>) objs.get("operations");
+        if (operations != null) {
+            List<CodegenOperation> ops = (List<CodegenOperation>) operations.get("operation");
+            for (CodegenOperation op : ops) {
+                if (op.hasConsumes) {
+                    if (!op.formParams.isEmpty() || op.isMultipart) {
+                        // DefaultCodegen only sets this if the first consumes mediaType
+                        // is application/x-www-form-urlencoded or multipart.
+                        // Can just use the original
+                        op.prioritizedContentTypes = op.consumes;
+                    } else {
+                        // Prioritize content types by moving application/json to the front
+                        // similar to JavaCodegen
+                        op.prioritizedContentTypes = prioritizeContentTypes(op.consumes);
+                        String mediaType = op.prioritizedContentTypes.get(0).get("mediaType");
+                        if (!DEFAULT_SUPPORTED_CONTENT_TYPES.contains(mediaType)) {
+                            LOGGER.warn("The media-type '{}' for operation '{}' is not support in the Dart generators by default.", mediaType, op.path);
+                        }
+                    }
+                }
+            }
+        }
+        return objs;
+    }
+
+    private List<Map<String, String>> prioritizeContentTypes(List<Map<String, String>> consumes) {
+        if (consumes.size() <= 1) {
+            // no need to change any order
+            return consumes;
+        }
+
+        List<Map<String, String>> prioritizedContentTypes = new ArrayList<>(consumes.size());
+
+        List<Map<String, String>> jsonVendorMimeTypes = new ArrayList<>(consumes.size());
+        List<Map<String, String>> jsonMimeTypes = new ArrayList<>(consumes.size());
+
+        for (Map<String, String> consume : consumes) {
+            String mediaType = consume.get("mediaType");
+            if (isJsonVendorMimeType(mediaType)) {
+                jsonVendorMimeTypes.add(consume);
+            } else if (isJsonMimeType(mediaType)) {
+                jsonMimeTypes.add(consume);
+            } else {
+                prioritizedContentTypes.add(consume);
+            }
+        }
+
+        prioritizedContentTypes.addAll(0, jsonMimeTypes);
+        prioritizedContentTypes.addAll(0, jsonVendorMimeTypes);
+        return prioritizedContentTypes;
+    }
+
+    private static boolean isMultipartType(String mediaType) {
+        if (mediaType != null) {
+            return "multipart/form-data".equals(mediaType);
+        }
+        return false;
+    }
+
     @Override
     protected void updateEnumVarsWithExtensions(List<Map<String, Object>> enumVars, Map<String, Object> vendorExtensions, String dataType) {
         if (vendorExtensions != null && useEnumExtension && vendorExtensions.containsKey("x-enum-values")) {
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioClientCodegen.java
index 23b50b2f756..517d1023b98 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioClientCodegen.java
@@ -264,7 +264,7 @@ public class DartDioClientCodegen extends AbstractDartCodegen {
 
     @Override
     public Map<String, Object> postProcessOperationsWithModels(Map<String, Object> objs, List<Object> allModels) {
-        objs = super.postProcessOperationsWithModels(objs, allModels);
+        super.postProcessOperationsWithModels(objs, allModels);
         Map<String, Object> operations = (Map<String, Object>) objs.get("operations");
         List<CodegenOperation> operationList = (List<CodegenOperation>) operations.get("operation");
 
@@ -272,24 +272,8 @@ public class DartDioClientCodegen extends AbstractDartCodegen {
         Set<String> resultImports = new HashSet<>();
 
         for (CodegenOperation op : operationList) {
-            op.httpMethod = op.httpMethod.toLowerCase(Locale.ROOT);
-            boolean isJson = true; //default to JSON
-            boolean isForm = false;
-            boolean isMultipart = false;
-            if (op.consumes != null) {
-                for (Map<String, String> consume : op.consumes) {
-                    if (consume.containsKey("mediaType")) {
-                        String type = consume.get("mediaType");
-                        isJson = type.equalsIgnoreCase("application/json");
-                        isForm = type.equalsIgnoreCase("application/x-www-form-urlencoded");
-                        isMultipart = type.equalsIgnoreCase("multipart/form-data");
-                        break;
-                    }
-                }
-            }
-
             for (CodegenParameter param : op.bodyParams) {
-                if (param.baseType != null && param.baseType.equalsIgnoreCase("Uint8List") && isMultipart) {
+                if (param.baseType != null && param.baseType.equalsIgnoreCase("Uint8List") && op.isMultipart) {
                     param.baseType = "MultipartFile";
                     param.dataType = "MultipartFile";
                 }
@@ -303,10 +287,6 @@ public class DartDioClientCodegen extends AbstractDartCodegen {
                 }
             }
 
-            op.vendorExtensions.put("x-is-json", isJson);
-            op.vendorExtensions.put("x-is-form", isForm);
-            op.vendorExtensions.put("x-is-multipart", isMultipart);
-
             resultImports.addAll(rewriteImports(op.imports));
             if (op.getHasFormParams()) {
                 resultImports.add("package:" + pubName + "/api_util.dart");
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioNextClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioNextClientCodegen.java
index 764c1146426..3beb4ca9a4a 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioNextClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioNextClientCodegen.java
@@ -305,7 +305,7 @@ public class DartDioNextClientCodegen extends AbstractDartCodegen {
 
     @Override
     public Map<String, Object> postProcessOperationsWithModels(Map<String, Object> objs, List<Object> allModels) {
-        objs = super.postProcessOperationsWithModels(objs, allModels);
+        super.postProcessOperationsWithModels(objs, allModels);
         Map<String, Object> operations = (Map<String, Object>) objs.get("operations");
         List<CodegenOperation> operationList = (List<CodegenOperation>) operations.get("operation");
 
@@ -313,24 +313,8 @@ public class DartDioNextClientCodegen extends AbstractDartCodegen {
         Set<String> resultImports = new HashSet<>();
 
         for (CodegenOperation op : operationList) {
-            op.httpMethod = op.httpMethod.toLowerCase(Locale.ROOT);
-            boolean isJson = true; //default to JSON
-            boolean isForm = false;
-            boolean isMultipart = false;
-            if (op.consumes != null) {
-                for (Map<String, String> consume : op.consumes) {
-                    if (consume.containsKey("mediaType")) {
-                        String type = consume.get("mediaType");
-                        isJson = type.equalsIgnoreCase("application/json");
-                        isForm = type.equalsIgnoreCase("application/x-www-form-urlencoded");
-                        isMultipart = type.equalsIgnoreCase("multipart/form-data");
-                        break;
-                    }
-                }
-            }
-
             for (CodegenParameter param : op.bodyParams) {
-                if (param.baseType != null && param.baseType.equalsIgnoreCase("Uint8List") && isMultipart) {
+                if (param.baseType != null && param.baseType.equalsIgnoreCase("Uint8List") && op.isMultipart) {
                     param.baseType = "MultipartFile";
                     param.dataType = "MultipartFile";
                 }
@@ -344,10 +328,6 @@ public class DartDioNextClientCodegen extends AbstractDartCodegen {
                 }
             }
 
-            op.vendorExtensions.put("x-is-json", isJson);
-            op.vendorExtensions.put("x-is-form", isForm);
-            op.vendorExtensions.put("x-is-multipart", isMultipart);
-
             resultImports.addAll(rewriteImports(op.imports));
             if (op.getHasFormParams()) {
                 resultImports.add("package:" + pubName + "/src/api_util.dart");
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 dff1dcd4235..522815498c5 100644
--- a/modules/openapi-generator/src/main/resources/dart-dio/api.mustache
+++ b/modules/openapi-generator/src/main/resources/dart-dio/api.mustache
@@ -63,10 +63,7 @@ class {{classname}} {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [{{^hasConsumes}}
-        'application/json',{{/hasConsumes}}{{#hasConsumes}}{{#consumes}}
-        '{{{mediaType}}}',{{/consumes}}{{/hasConsumes}}
-      ].first,
+      contentType: '{{^hasConsumes}}application/json{{/hasConsumes}}{{#hasConsumes}}{{#prioritizedContentTypes}}{{#-first}}{{{mediaType}}}{{/-first}}{{/prioritizedContentTypes}}{{/hasConsumes}}',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/api.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/api.mustache
index 34cf9554991..b019de39c66 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/api.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/api.mustache
@@ -60,11 +60,8 @@ class {{classname}} {
           },{{/authMethods}}
         ],{{/hasAuthMethods}}
         ...?extra,
-      },
-      contentType: [{{^hasConsumes}}
-        'application/json',{{/hasConsumes}}{{#hasConsumes}}{{#consumes}}
-        '{{{mediaType}}}',{{/consumes}}{{/hasConsumes}}
-      ].first,
+      },{{#hasConsumes}}
+      contentType: '{{#prioritizedContentTypes}}{{#-first}}{{{mediaType}}}{{/-first}}{{/prioritizedContentTypes}}',{{/hasConsumes}}
       validateStatus: validateStatus,
     );
 
diff --git a/modules/openapi-generator/src/main/resources/dart2/api.mustache b/modules/openapi-generator/src/main/resources/dart2/api.mustache
index 6a53829cb59..a7bb9289143 100644
--- a/modules/openapi-generator/src/main/resources/dart2/api.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/api.mustache
@@ -95,7 +95,7 @@ class {{{classname}}} {
       {{/headerParams}}
     {{/hasHeaderParams}}
 
-    final contentTypes = <String>[{{#consumes}}'{{{mediaType}}}'{{^-last}}, {{/-last}}{{/consumes}}];
+    final contentTypes = <String>[{{#prioritizedContentTypes}}'{{{mediaType}}}'{{^-last}}, {{/-last}}{{/prioritizedContentTypes}}];
     final nullableContentType = contentTypes.isNotEmpty ? contentTypes[0] : null;
     final authNames = <String>[{{#authMethods}}'{{{name}}}'{{^-last}}, {{/-last}}{{/authMethods}}];
 
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/README.md b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/README.md
index f49dd295950..31cdc5ce99b 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/README.md
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/README.md
@@ -64,46 +64,46 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Class | Method | HTTP request | Description
 ------------ | ------------- | ------------- | -------------
-*AnotherFakeApi* | [**call123testSpecialTags**](doc/AnotherFakeApi.md#call123testspecialtags) | **patch** /another-fake/dummy | To test special tags
-*DefaultApi* | [**fooGet**](doc/DefaultApi.md#fooget) | **get** /foo | 
-*FakeApi* | [**fakeHealthGet**](doc/FakeApi.md#fakehealthget) | **get** /fake/health | Health check endpoint
-*FakeApi* | [**fakeHttpSignatureTest**](doc/FakeApi.md#fakehttpsignaturetest) | **get** /fake/http-signature-test | test http signature authentication
-*FakeApi* | [**fakeOuterBooleanSerialize**](doc/FakeApi.md#fakeouterbooleanserialize) | **post** /fake/outer/boolean | 
-*FakeApi* | [**fakeOuterCompositeSerialize**](doc/FakeApi.md#fakeoutercompositeserialize) | **post** /fake/outer/composite | 
-*FakeApi* | [**fakeOuterNumberSerialize**](doc/FakeApi.md#fakeouternumberserialize) | **post** /fake/outer/number | 
-*FakeApi* | [**fakeOuterStringSerialize**](doc/FakeApi.md#fakeouterstringserialize) | **post** /fake/outer/string | 
-*FakeApi* | [**fakePropertyEnumIntegerSerialize**](doc/FakeApi.md#fakepropertyenumintegerserialize) | **post** /fake/property/enum-int | 
-*FakeApi* | [**testBodyWithFileSchema**](doc/FakeApi.md#testbodywithfileschema) | **put** /fake/body-with-file-schema | 
-*FakeApi* | [**testBodyWithQueryParams**](doc/FakeApi.md#testbodywithqueryparams) | **put** /fake/body-with-query-params | 
-*FakeApi* | [**testClientModel**](doc/FakeApi.md#testclientmodel) | **patch** /fake | To test \&quot;client\&quot; model
-*FakeApi* | [**testEndpointParameters**](doc/FakeApi.md#testendpointparameters) | **post** /fake | Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트 
-*FakeApi* | [**testEnumParameters**](doc/FakeApi.md#testenumparameters) | **get** /fake | To test enum parameters
-*FakeApi* | [**testGroupParameters**](doc/FakeApi.md#testgroupparameters) | **delete** /fake | Fake endpoint to test group parameters (optional)
-*FakeApi* | [**testInlineAdditionalProperties**](doc/FakeApi.md#testinlineadditionalproperties) | **post** /fake/inline-additionalProperties | test inline additionalProperties
-*FakeApi* | [**testJsonFormData**](doc/FakeApi.md#testjsonformdata) | **get** /fake/jsonFormData | test json serialization of form data
-*FakeApi* | [**testQueryParameterCollectionFormat**](doc/FakeApi.md#testqueryparametercollectionformat) | **put** /fake/test-query-paramters | 
-*FakeClassnameTags123Api* | [**testClassname**](doc/FakeClassnameTags123Api.md#testclassname) | **patch** /fake_classname_test | To test class name in snake case
-*PetApi* | [**addPet**](doc/PetApi.md#addpet) | **post** /pet | Add a new pet to the store
-*PetApi* | [**deletePet**](doc/PetApi.md#deletepet) | **delete** /pet/{petId} | Deletes a pet
-*PetApi* | [**findPetsByStatus**](doc/PetApi.md#findpetsbystatus) | **get** /pet/findByStatus | Finds Pets by status
-*PetApi* | [**findPetsByTags**](doc/PetApi.md#findpetsbytags) | **get** /pet/findByTags | Finds Pets by tags
-*PetApi* | [**getPetById**](doc/PetApi.md#getpetbyid) | **get** /pet/{petId} | Find pet by ID
-*PetApi* | [**updatePet**](doc/PetApi.md#updatepet) | **put** /pet | Update an existing pet
-*PetApi* | [**updatePetWithForm**](doc/PetApi.md#updatepetwithform) | **post** /pet/{petId} | Updates a pet in the store with form data
-*PetApi* | [**uploadFile**](doc/PetApi.md#uploadfile) | **post** /pet/{petId}/uploadImage | uploads an image
-*PetApi* | [**uploadFileWithRequiredFile**](doc/PetApi.md#uploadfilewithrequiredfile) | **post** /fake/{petId}/uploadImageWithRequiredFile | uploads an image (required)
-*StoreApi* | [**deleteOrder**](doc/StoreApi.md#deleteorder) | **delete** /store/order/{order_id} | Delete purchase order by ID
-*StoreApi* | [**getInventory**](doc/StoreApi.md#getinventory) | **get** /store/inventory | Returns pet inventories by status
-*StoreApi* | [**getOrderById**](doc/StoreApi.md#getorderbyid) | **get** /store/order/{order_id} | Find purchase order by ID
-*StoreApi* | [**placeOrder**](doc/StoreApi.md#placeorder) | **post** /store/order | Place an order for a pet
-*UserApi* | [**createUser**](doc/UserApi.md#createuser) | **post** /user | Create user
-*UserApi* | [**createUsersWithArrayInput**](doc/UserApi.md#createuserswitharrayinput) | **post** /user/createWithArray | Creates list of users with given input array
-*UserApi* | [**createUsersWithListInput**](doc/UserApi.md#createuserswithlistinput) | **post** /user/createWithList | Creates list of users with given input array
-*UserApi* | [**deleteUser**](doc/UserApi.md#deleteuser) | **delete** /user/{username} | Delete user
-*UserApi* | [**getUserByName**](doc/UserApi.md#getuserbyname) | **get** /user/{username} | Get user by user name
-*UserApi* | [**loginUser**](doc/UserApi.md#loginuser) | **get** /user/login | Logs user into the system
-*UserApi* | [**logoutUser**](doc/UserApi.md#logoutuser) | **get** /user/logout | Logs out current logged in user session
-*UserApi* | [**updateUser**](doc/UserApi.md#updateuser) | **put** /user/{username} | Updated user
+*AnotherFakeApi* | [**call123testSpecialTags**](doc/AnotherFakeApi.md#call123testspecialtags) | **PATCH** /another-fake/dummy | To test special tags
+*DefaultApi* | [**fooGet**](doc/DefaultApi.md#fooget) | **GET** /foo | 
+*FakeApi* | [**fakeHealthGet**](doc/FakeApi.md#fakehealthget) | **GET** /fake/health | Health check endpoint
+*FakeApi* | [**fakeHttpSignatureTest**](doc/FakeApi.md#fakehttpsignaturetest) | **GET** /fake/http-signature-test | test http signature authentication
+*FakeApi* | [**fakeOuterBooleanSerialize**](doc/FakeApi.md#fakeouterbooleanserialize) | **POST** /fake/outer/boolean | 
+*FakeApi* | [**fakeOuterCompositeSerialize**](doc/FakeApi.md#fakeoutercompositeserialize) | **POST** /fake/outer/composite | 
+*FakeApi* | [**fakeOuterNumberSerialize**](doc/FakeApi.md#fakeouternumberserialize) | **POST** /fake/outer/number | 
+*FakeApi* | [**fakeOuterStringSerialize**](doc/FakeApi.md#fakeouterstringserialize) | **POST** /fake/outer/string | 
+*FakeApi* | [**fakePropertyEnumIntegerSerialize**](doc/FakeApi.md#fakepropertyenumintegerserialize) | **POST** /fake/property/enum-int | 
+*FakeApi* | [**testBodyWithFileSchema**](doc/FakeApi.md#testbodywithfileschema) | **PUT** /fake/body-with-file-schema | 
+*FakeApi* | [**testBodyWithQueryParams**](doc/FakeApi.md#testbodywithqueryparams) | **PUT** /fake/body-with-query-params | 
+*FakeApi* | [**testClientModel**](doc/FakeApi.md#testclientmodel) | **PATCH** /fake | To test \&quot;client\&quot; model
+*FakeApi* | [**testEndpointParameters**](doc/FakeApi.md#testendpointparameters) | **POST** /fake | Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트 
+*FakeApi* | [**testEnumParameters**](doc/FakeApi.md#testenumparameters) | **GET** /fake | To test enum parameters
+*FakeApi* | [**testGroupParameters**](doc/FakeApi.md#testgroupparameters) | **DELETE** /fake | Fake endpoint to test group parameters (optional)
+*FakeApi* | [**testInlineAdditionalProperties**](doc/FakeApi.md#testinlineadditionalproperties) | **POST** /fake/inline-additionalProperties | test inline additionalProperties
+*FakeApi* | [**testJsonFormData**](doc/FakeApi.md#testjsonformdata) | **GET** /fake/jsonFormData | test json serialization of form data
+*FakeApi* | [**testQueryParameterCollectionFormat**](doc/FakeApi.md#testqueryparametercollectionformat) | **PUT** /fake/test-query-paramters | 
+*FakeClassnameTags123Api* | [**testClassname**](doc/FakeClassnameTags123Api.md#testclassname) | **PATCH** /fake_classname_test | To test class name in snake case
+*PetApi* | [**addPet**](doc/PetApi.md#addpet) | **POST** /pet | Add a new pet to the store
+*PetApi* | [**deletePet**](doc/PetApi.md#deletepet) | **DELETE** /pet/{petId} | Deletes a pet
+*PetApi* | [**findPetsByStatus**](doc/PetApi.md#findpetsbystatus) | **GET** /pet/findByStatus | Finds Pets by status
+*PetApi* | [**findPetsByTags**](doc/PetApi.md#findpetsbytags) | **GET** /pet/findByTags | Finds Pets by tags
+*PetApi* | [**getPetById**](doc/PetApi.md#getpetbyid) | **GET** /pet/{petId} | Find pet by ID
+*PetApi* | [**updatePet**](doc/PetApi.md#updatepet) | **PUT** /pet | Update an existing pet
+*PetApi* | [**updatePetWithForm**](doc/PetApi.md#updatepetwithform) | **POST** /pet/{petId} | Updates a pet in the store with form data
+*PetApi* | [**uploadFile**](doc/PetApi.md#uploadfile) | **POST** /pet/{petId}/uploadImage | uploads an image
+*PetApi* | [**uploadFileWithRequiredFile**](doc/PetApi.md#uploadfilewithrequiredfile) | **POST** /fake/{petId}/uploadImageWithRequiredFile | uploads an image (required)
+*StoreApi* | [**deleteOrder**](doc/StoreApi.md#deleteorder) | **DELETE** /store/order/{order_id} | Delete purchase order by ID
+*StoreApi* | [**getInventory**](doc/StoreApi.md#getinventory) | **GET** /store/inventory | Returns pet inventories by status
+*StoreApi* | [**getOrderById**](doc/StoreApi.md#getorderbyid) | **GET** /store/order/{order_id} | Find purchase order by ID
+*StoreApi* | [**placeOrder**](doc/StoreApi.md#placeorder) | **POST** /store/order | Place an order for a pet
+*UserApi* | [**createUser**](doc/UserApi.md#createuser) | **POST** /user | Create user
+*UserApi* | [**createUsersWithArrayInput**](doc/UserApi.md#createuserswitharrayinput) | **POST** /user/createWithArray | Creates list of users with given input array
+*UserApi* | [**createUsersWithListInput**](doc/UserApi.md#createuserswithlistinput) | **POST** /user/createWithList | Creates list of users with given input array
+*UserApi* | [**deleteUser**](doc/UserApi.md#deleteuser) | **DELETE** /user/{username} | Delete user
+*UserApi* | [**getUserByName**](doc/UserApi.md#getuserbyname) | **GET** /user/{username} | Get user by user name
+*UserApi* | [**loginUser**](doc/UserApi.md#loginuser) | **GET** /user/login | Logs user into the system
+*UserApi* | [**logoutUser**](doc/UserApi.md#logoutuser) | **GET** /user/logout | Logs out current logged in user session
+*UserApi* | [**updateUser**](doc/UserApi.md#updateuser) | **PUT** /user/{username} | Updated user
 
 
 ## Documentation For Models
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/AnotherFakeApi.md b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/AnotherFakeApi.md
index d55663297c1..bb401f7c20c 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/AnotherFakeApi.md
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/AnotherFakeApi.md
@@ -9,7 +9,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**call123testSpecialTags**](AnotherFakeApi.md#call123testspecialtags) | **patch** /another-fake/dummy | To test special tags
+[**call123testSpecialTags**](AnotherFakeApi.md#call123testspecialtags) | **PATCH** /another-fake/dummy | To test special tags
 
 
 # **call123testSpecialTags**
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/DefaultApi.md b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/DefaultApi.md
index be916c3037d..5c305ecaa71 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/DefaultApi.md
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/DefaultApi.md
@@ -9,7 +9,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**fooGet**](DefaultApi.md#fooget) | **get** /foo | 
+[**fooGet**](DefaultApi.md#fooget) | **GET** /foo | 
 
 
 # **fooGet**
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/FakeApi.md b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/FakeApi.md
index c01cc40f97d..8ceda8fa68d 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/FakeApi.md
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/FakeApi.md
@@ -9,22 +9,22 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**fakeHealthGet**](FakeApi.md#fakehealthget) | **get** /fake/health | Health check endpoint
-[**fakeHttpSignatureTest**](FakeApi.md#fakehttpsignaturetest) | **get** /fake/http-signature-test | test http signature authentication
-[**fakeOuterBooleanSerialize**](FakeApi.md#fakeouterbooleanserialize) | **post** /fake/outer/boolean | 
-[**fakeOuterCompositeSerialize**](FakeApi.md#fakeoutercompositeserialize) | **post** /fake/outer/composite | 
-[**fakeOuterNumberSerialize**](FakeApi.md#fakeouternumberserialize) | **post** /fake/outer/number | 
-[**fakeOuterStringSerialize**](FakeApi.md#fakeouterstringserialize) | **post** /fake/outer/string | 
-[**fakePropertyEnumIntegerSerialize**](FakeApi.md#fakepropertyenumintegerserialize) | **post** /fake/property/enum-int | 
-[**testBodyWithFileSchema**](FakeApi.md#testbodywithfileschema) | **put** /fake/body-with-file-schema | 
-[**testBodyWithQueryParams**](FakeApi.md#testbodywithqueryparams) | **put** /fake/body-with-query-params | 
-[**testClientModel**](FakeApi.md#testclientmodel) | **patch** /fake | To test \&quot;client\&quot; model
-[**testEndpointParameters**](FakeApi.md#testendpointparameters) | **post** /fake | Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트 
-[**testEnumParameters**](FakeApi.md#testenumparameters) | **get** /fake | To test enum parameters
-[**testGroupParameters**](FakeApi.md#testgroupparameters) | **delete** /fake | Fake endpoint to test group parameters (optional)
-[**testInlineAdditionalProperties**](FakeApi.md#testinlineadditionalproperties) | **post** /fake/inline-additionalProperties | test inline additionalProperties
-[**testJsonFormData**](FakeApi.md#testjsonformdata) | **get** /fake/jsonFormData | test json serialization of form data
-[**testQueryParameterCollectionFormat**](FakeApi.md#testqueryparametercollectionformat) | **put** /fake/test-query-paramters | 
+[**fakeHealthGet**](FakeApi.md#fakehealthget) | **GET** /fake/health | Health check endpoint
+[**fakeHttpSignatureTest**](FakeApi.md#fakehttpsignaturetest) | **GET** /fake/http-signature-test | test http signature authentication
+[**fakeOuterBooleanSerialize**](FakeApi.md#fakeouterbooleanserialize) | **POST** /fake/outer/boolean | 
+[**fakeOuterCompositeSerialize**](FakeApi.md#fakeoutercompositeserialize) | **POST** /fake/outer/composite | 
+[**fakeOuterNumberSerialize**](FakeApi.md#fakeouternumberserialize) | **POST** /fake/outer/number | 
+[**fakeOuterStringSerialize**](FakeApi.md#fakeouterstringserialize) | **POST** /fake/outer/string | 
+[**fakePropertyEnumIntegerSerialize**](FakeApi.md#fakepropertyenumintegerserialize) | **POST** /fake/property/enum-int | 
+[**testBodyWithFileSchema**](FakeApi.md#testbodywithfileschema) | **PUT** /fake/body-with-file-schema | 
+[**testBodyWithQueryParams**](FakeApi.md#testbodywithqueryparams) | **PUT** /fake/body-with-query-params | 
+[**testClientModel**](FakeApi.md#testclientmodel) | **PATCH** /fake | To test \&quot;client\&quot; model
+[**testEndpointParameters**](FakeApi.md#testendpointparameters) | **POST** /fake | Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트 
+[**testEnumParameters**](FakeApi.md#testenumparameters) | **GET** /fake | To test enum parameters
+[**testGroupParameters**](FakeApi.md#testgroupparameters) | **DELETE** /fake | Fake endpoint to test group parameters (optional)
+[**testInlineAdditionalProperties**](FakeApi.md#testinlineadditionalproperties) | **POST** /fake/inline-additionalProperties | test inline additionalProperties
+[**testJsonFormData**](FakeApi.md#testjsonformdata) | **GET** /fake/jsonFormData | test json serialization of form data
+[**testQueryParameterCollectionFormat**](FakeApi.md#testqueryparametercollectionformat) | **PUT** /fake/test-query-paramters | 
 
 
 # **fakeHealthGet**
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/FakeClassnameTags123Api.md b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/FakeClassnameTags123Api.md
index 9745ca8e3ff..98fe0b47358 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/FakeClassnameTags123Api.md
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/FakeClassnameTags123Api.md
@@ -9,7 +9,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**testClassname**](FakeClassnameTags123Api.md#testclassname) | **patch** /fake_classname_test | To test class name in snake case
+[**testClassname**](FakeClassnameTags123Api.md#testclassname) | **PATCH** /fake_classname_test | To test class name in snake case
 
 
 # **testClassname**
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/PetApi.md b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/PetApi.md
index d5a07d5046e..841eed63291 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/PetApi.md
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/PetApi.md
@@ -9,15 +9,15 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**addPet**](PetApi.md#addpet) | **post** /pet | Add a new pet to the store
-[**deletePet**](PetApi.md#deletepet) | **delete** /pet/{petId} | Deletes a pet
-[**findPetsByStatus**](PetApi.md#findpetsbystatus) | **get** /pet/findByStatus | Finds Pets by status
-[**findPetsByTags**](PetApi.md#findpetsbytags) | **get** /pet/findByTags | Finds Pets by tags
-[**getPetById**](PetApi.md#getpetbyid) | **get** /pet/{petId} | Find pet by ID
-[**updatePet**](PetApi.md#updatepet) | **put** /pet | Update an existing pet
-[**updatePetWithForm**](PetApi.md#updatepetwithform) | **post** /pet/{petId} | Updates a pet in the store with form data
-[**uploadFile**](PetApi.md#uploadfile) | **post** /pet/{petId}/uploadImage | uploads an image
-[**uploadFileWithRequiredFile**](PetApi.md#uploadfilewithrequiredfile) | **post** /fake/{petId}/uploadImageWithRequiredFile | uploads an image (required)
+[**addPet**](PetApi.md#addpet) | **POST** /pet | Add a new pet to the store
+[**deletePet**](PetApi.md#deletepet) | **DELETE** /pet/{petId} | Deletes a pet
+[**findPetsByStatus**](PetApi.md#findpetsbystatus) | **GET** /pet/findByStatus | Finds Pets by status
+[**findPetsByTags**](PetApi.md#findpetsbytags) | **GET** /pet/findByTags | Finds Pets by tags
+[**getPetById**](PetApi.md#getpetbyid) | **GET** /pet/{petId} | Find pet by ID
+[**updatePet**](PetApi.md#updatepet) | **PUT** /pet | Update an existing pet
+[**updatePetWithForm**](PetApi.md#updatepetwithform) | **POST** /pet/{petId} | Updates a pet in the store with form data
+[**uploadFile**](PetApi.md#uploadfile) | **POST** /pet/{petId}/uploadImage | uploads an image
+[**uploadFileWithRequiredFile**](PetApi.md#uploadfilewithrequiredfile) | **POST** /fake/{petId}/uploadImageWithRequiredFile | uploads an image (required)
 
 
 # **addPet**
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/StoreApi.md b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/StoreApi.md
index 1fcb8f71eea..a7dbf9ad019 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/StoreApi.md
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/StoreApi.md
@@ -9,10 +9,10 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**deleteOrder**](StoreApi.md#deleteorder) | **delete** /store/order/{order_id} | Delete purchase order by ID
-[**getInventory**](StoreApi.md#getinventory) | **get** /store/inventory | Returns pet inventories by status
-[**getOrderById**](StoreApi.md#getorderbyid) | **get** /store/order/{order_id} | Find purchase order by ID
-[**placeOrder**](StoreApi.md#placeorder) | **post** /store/order | Place an order for a pet
+[**deleteOrder**](StoreApi.md#deleteorder) | **DELETE** /store/order/{order_id} | Delete purchase order by ID
+[**getInventory**](StoreApi.md#getinventory) | **GET** /store/inventory | Returns pet inventories by status
+[**getOrderById**](StoreApi.md#getorderbyid) | **GET** /store/order/{order_id} | Find purchase order by ID
+[**placeOrder**](StoreApi.md#placeorder) | **POST** /store/order | Place an order for a pet
 
 
 # **deleteOrder**
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/UserApi.md b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/UserApi.md
index 62e01652e80..32bc2e675da 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/UserApi.md
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/doc/UserApi.md
@@ -9,14 +9,14 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**createUser**](UserApi.md#createuser) | **post** /user | Create user
-[**createUsersWithArrayInput**](UserApi.md#createuserswitharrayinput) | **post** /user/createWithArray | Creates list of users with given input array
-[**createUsersWithListInput**](UserApi.md#createuserswithlistinput) | **post** /user/createWithList | Creates list of users with given input array
-[**deleteUser**](UserApi.md#deleteuser) | **delete** /user/{username} | Delete user
-[**getUserByName**](UserApi.md#getuserbyname) | **get** /user/{username} | Get user by user name
-[**loginUser**](UserApi.md#loginuser) | **get** /user/login | Logs user into the system
-[**logoutUser**](UserApi.md#logoutuser) | **get** /user/logout | Logs out current logged in user session
-[**updateUser**](UserApi.md#updateuser) | **put** /user/{username} | Updated user
+[**createUser**](UserApi.md#createuser) | **POST** /user | Create user
+[**createUsersWithArrayInput**](UserApi.md#createuserswitharrayinput) | **POST** /user/createWithArray | Creates list of users with given input array
+[**createUsersWithListInput**](UserApi.md#createuserswithlistinput) | **POST** /user/createWithList | Creates list of users with given input array
+[**deleteUser**](UserApi.md#deleteuser) | **DELETE** /user/{username} | Delete user
+[**getUserByName**](UserApi.md#getuserbyname) | **GET** /user/{username} | Get user by user name
+[**loginUser**](UserApi.md#loginuser) | **GET** /user/login | Logs user into the system
+[**logoutUser**](UserApi.md#logoutuser) | **GET** /user/logout | Logs out current logged in user session
+[**updateUser**](UserApi.md#updateuser) | **PUT** /user/{username} | Updated user
 
 
 # **createUser**
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/another_fake_api.dart b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/another_fake_api.dart
index 00d88a5c178..6730b6925ad 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/another_fake_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/another_fake_api.dart
@@ -39,9 +39,7 @@ class AnotherFakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/default_api.dart b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/default_api.dart
index 48fc9b8c444..1311f160e5b 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/default_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/default_api.dart
@@ -38,9 +38,6 @@ class DefaultApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/fake_api.dart b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/fake_api.dart
index fed890a78c1..c3915495c81 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/fake_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/fake_api.dart
@@ -48,9 +48,6 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -126,10 +123,7 @@ class FakeApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-        'application/xml',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -190,9 +184,7 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -274,9 +266,7 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -363,9 +353,7 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -447,9 +435,7 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -531,9 +517,7 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -620,9 +604,7 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -683,9 +665,7 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -746,9 +726,7 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -853,9 +831,7 @@ class FakeApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/x-www-form-urlencoded',
-      ].first,
+      contentType: 'application/x-www-form-urlencoded',
       validateStatus: validateStatus,
     );
 
@@ -938,9 +914,7 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/x-www-form-urlencoded',
-      ].first,
+      contentType: 'application/x-www-form-urlencoded',
       validateStatus: validateStatus,
     );
 
@@ -1018,9 +992,6 @@ class FakeApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -1065,9 +1036,7 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -1128,9 +1097,7 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/x-www-form-urlencoded',
-      ].first,
+      contentType: 'application/x-www-form-urlencoded',
       validateStatus: validateStatus,
     );
 
@@ -1196,9 +1163,6 @@ class FakeApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/fake_classname_tags123_api.dart b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/fake_classname_tags123_api.dart
index 01d0383fd16..a2b5a816bab 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/fake_classname_tags123_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/fake_classname_tags123_api.dart
@@ -46,9 +46,7 @@ class FakeClassnameTags123Api {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/pet_api.dart b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/pet_api.dart
index 219b0cecd26..8a684092fc2 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/pet_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/pet_api.dart
@@ -48,10 +48,7 @@ class PetApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-        'application/xml',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -118,9 +115,6 @@ class PetApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -166,9 +160,6 @@ class PetApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -242,9 +233,6 @@ class PetApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -320,9 +308,6 @@ class PetApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -395,10 +380,7 @@ class PetApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-        'application/xml',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -465,9 +447,7 @@ class PetApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/x-www-form-urlencoded',
-      ].first,
+      contentType: 'application/x-www-form-urlencoded',
       validateStatus: validateStatus,
     );
 
@@ -536,9 +516,7 @@ class PetApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'multipart/form-data',
-      ].first,
+      contentType: 'multipart/form-data',
       validateStatus: validateStatus,
     );
 
@@ -634,9 +612,7 @@ class PetApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'multipart/form-data',
-      ].first,
+      contentType: 'multipart/form-data',
       validateStatus: validateStatus,
     );
 
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/store_api.dart b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/store_api.dart
index 0c0b9f44794..3b77dd62607 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/store_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/store_api.dart
@@ -40,9 +40,6 @@ class StoreApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -89,9 +86,6 @@ class StoreApi {
         ],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -159,9 +153,6 @@ class StoreApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -229,9 +220,7 @@ class StoreApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
diff --git a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/user_api.dart b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/user_api.dart
index c0551df5e51..ebfb06b1c97 100644
--- a/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/user_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/api/user_api.dart
@@ -40,9 +40,7 @@ class UserApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -102,9 +100,7 @@ class UserApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -164,9 +160,7 @@ class UserApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
@@ -226,9 +220,6 @@ class UserApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -269,9 +260,6 @@ class UserApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -340,9 +328,6 @@ class UserApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -407,9 +392,6 @@ class UserApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
       validateStatus: validateStatus,
     );
 
@@ -451,9 +433,7 @@ class UserApi {
         'secure': <Map<String, String>>[],
         ...?extra,
       },
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       validateStatus: validateStatus,
     );
 
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/README.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/README.md
index af1b22de4d5..ac04fa9f72b 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/README.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/README.md
@@ -58,26 +58,26 @@ All URIs are relative to *http://petstore.swagger.io/v2*
 
 Class | Method | HTTP request | Description
 ------------ | ------------- | ------------- | -------------
-*PetApi* | [**addPet**](doc/PetApi.md#addpet) | **post** /pet | Add a new pet to the store
-*PetApi* | [**deletePet**](doc/PetApi.md#deletepet) | **delete** /pet/{petId} | Deletes a pet
-*PetApi* | [**findPetsByStatus**](doc/PetApi.md#findpetsbystatus) | **get** /pet/findByStatus | Finds Pets by status
-*PetApi* | [**findPetsByTags**](doc/PetApi.md#findpetsbytags) | **get** /pet/findByTags | Finds Pets by tags
-*PetApi* | [**getPetById**](doc/PetApi.md#getpetbyid) | **get** /pet/{petId} | Find pet by ID
-*PetApi* | [**updatePet**](doc/PetApi.md#updatepet) | **put** /pet | Update an existing pet
-*PetApi* | [**updatePetWithForm**](doc/PetApi.md#updatepetwithform) | **post** /pet/{petId} | Updates a pet in the store with form data
-*PetApi* | [**uploadFile**](doc/PetApi.md#uploadfile) | **post** /pet/{petId}/uploadImage | uploads an image
-*StoreApi* | [**deleteOrder**](doc/StoreApi.md#deleteorder) | **delete** /store/order/{orderId} | Delete purchase order by ID
-*StoreApi* | [**getInventory**](doc/StoreApi.md#getinventory) | **get** /store/inventory | Returns pet inventories by status
-*StoreApi* | [**getOrderById**](doc/StoreApi.md#getorderbyid) | **get** /store/order/{orderId} | Find purchase order by ID
-*StoreApi* | [**placeOrder**](doc/StoreApi.md#placeorder) | **post** /store/order | Place an order for a pet
-*UserApi* | [**createUser**](doc/UserApi.md#createuser) | **post** /user | Create user
-*UserApi* | [**createUsersWithArrayInput**](doc/UserApi.md#createuserswitharrayinput) | **post** /user/createWithArray | Creates list of users with given input array
-*UserApi* | [**createUsersWithListInput**](doc/UserApi.md#createuserswithlistinput) | **post** /user/createWithList | Creates list of users with given input array
-*UserApi* | [**deleteUser**](doc/UserApi.md#deleteuser) | **delete** /user/{username} | Delete user
-*UserApi* | [**getUserByName**](doc/UserApi.md#getuserbyname) | **get** /user/{username} | Get user by user name
-*UserApi* | [**loginUser**](doc/UserApi.md#loginuser) | **get** /user/login | Logs user into the system
-*UserApi* | [**logoutUser**](doc/UserApi.md#logoutuser) | **get** /user/logout | Logs out current logged in user session
-*UserApi* | [**updateUser**](doc/UserApi.md#updateuser) | **put** /user/{username} | Updated user
+*PetApi* | [**addPet**](doc/PetApi.md#addpet) | **POST** /pet | Add a new pet to the store
+*PetApi* | [**deletePet**](doc/PetApi.md#deletepet) | **DELETE** /pet/{petId} | Deletes a pet
+*PetApi* | [**findPetsByStatus**](doc/PetApi.md#findpetsbystatus) | **GET** /pet/findByStatus | Finds Pets by status
+*PetApi* | [**findPetsByTags**](doc/PetApi.md#findpetsbytags) | **GET** /pet/findByTags | Finds Pets by tags
+*PetApi* | [**getPetById**](doc/PetApi.md#getpetbyid) | **GET** /pet/{petId} | Find pet by ID
+*PetApi* | [**updatePet**](doc/PetApi.md#updatepet) | **PUT** /pet | Update an existing pet
+*PetApi* | [**updatePetWithForm**](doc/PetApi.md#updatepetwithform) | **POST** /pet/{petId} | Updates a pet in the store with form data
+*PetApi* | [**uploadFile**](doc/PetApi.md#uploadfile) | **POST** /pet/{petId}/uploadImage | uploads an image
+*StoreApi* | [**deleteOrder**](doc/StoreApi.md#deleteorder) | **DELETE** /store/order/{orderId} | Delete purchase order by ID
+*StoreApi* | [**getInventory**](doc/StoreApi.md#getinventory) | **GET** /store/inventory | Returns pet inventories by status
+*StoreApi* | [**getOrderById**](doc/StoreApi.md#getorderbyid) | **GET** /store/order/{orderId} | Find purchase order by ID
+*StoreApi* | [**placeOrder**](doc/StoreApi.md#placeorder) | **POST** /store/order | Place an order for a pet
+*UserApi* | [**createUser**](doc/UserApi.md#createuser) | **POST** /user | Create user
+*UserApi* | [**createUsersWithArrayInput**](doc/UserApi.md#createuserswitharrayinput) | **POST** /user/createWithArray | Creates list of users with given input array
+*UserApi* | [**createUsersWithListInput**](doc/UserApi.md#createuserswithlistinput) | **POST** /user/createWithList | Creates list of users with given input array
+*UserApi* | [**deleteUser**](doc/UserApi.md#deleteuser) | **DELETE** /user/{username} | Delete user
+*UserApi* | [**getUserByName**](doc/UserApi.md#getuserbyname) | **GET** /user/{username} | Get user by user name
+*UserApi* | [**loginUser**](doc/UserApi.md#loginuser) | **GET** /user/login | Logs user into the system
+*UserApi* | [**logoutUser**](doc/UserApi.md#logoutuser) | **GET** /user/logout | Logs out current logged in user session
+*UserApi* | [**updateUser**](doc/UserApi.md#updateuser) | **PUT** /user/{username} | Updated user
 
 
 ## Documentation For Models
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/PetApi.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/PetApi.md
index 3a78296f383..74c87b72acc 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/PetApi.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/PetApi.md
@@ -9,14 +9,14 @@ All URIs are relative to *http://petstore.swagger.io/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**addPet**](PetApi.md#addpet) | **post** /pet | Add a new pet to the store
-[**deletePet**](PetApi.md#deletepet) | **delete** /pet/{petId} | Deletes a pet
-[**findPetsByStatus**](PetApi.md#findpetsbystatus) | **get** /pet/findByStatus | Finds Pets by status
-[**findPetsByTags**](PetApi.md#findpetsbytags) | **get** /pet/findByTags | Finds Pets by tags
-[**getPetById**](PetApi.md#getpetbyid) | **get** /pet/{petId} | Find pet by ID
-[**updatePet**](PetApi.md#updatepet) | **put** /pet | Update an existing pet
-[**updatePetWithForm**](PetApi.md#updatepetwithform) | **post** /pet/{petId} | Updates a pet in the store with form data
-[**uploadFile**](PetApi.md#uploadfile) | **post** /pet/{petId}/uploadImage | uploads an image
+[**addPet**](PetApi.md#addpet) | **POST** /pet | Add a new pet to the store
+[**deletePet**](PetApi.md#deletepet) | **DELETE** /pet/{petId} | Deletes a pet
+[**findPetsByStatus**](PetApi.md#findpetsbystatus) | **GET** /pet/findByStatus | Finds Pets by status
+[**findPetsByTags**](PetApi.md#findpetsbytags) | **GET** /pet/findByTags | Finds Pets by tags
+[**getPetById**](PetApi.md#getpetbyid) | **GET** /pet/{petId} | Find pet by ID
+[**updatePet**](PetApi.md#updatepet) | **PUT** /pet | Update an existing pet
+[**updatePetWithForm**](PetApi.md#updatepetwithform) | **POST** /pet/{petId} | Updates a pet in the store with form data
+[**uploadFile**](PetApi.md#uploadfile) | **POST** /pet/{petId}/uploadImage | uploads an image
 
 
 # **addPet**
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/StoreApi.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/StoreApi.md
index 0b016d70a84..6075223c741 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/StoreApi.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/StoreApi.md
@@ -9,10 +9,10 @@ All URIs are relative to *http://petstore.swagger.io/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**deleteOrder**](StoreApi.md#deleteorder) | **delete** /store/order/{orderId} | Delete purchase order by ID
-[**getInventory**](StoreApi.md#getinventory) | **get** /store/inventory | Returns pet inventories by status
-[**getOrderById**](StoreApi.md#getorderbyid) | **get** /store/order/{orderId} | Find purchase order by ID
-[**placeOrder**](StoreApi.md#placeorder) | **post** /store/order | Place an order for a pet
+[**deleteOrder**](StoreApi.md#deleteorder) | **DELETE** /store/order/{orderId} | Delete purchase order by ID
+[**getInventory**](StoreApi.md#getinventory) | **GET** /store/inventory | Returns pet inventories by status
+[**getOrderById**](StoreApi.md#getorderbyid) | **GET** /store/order/{orderId} | Find purchase order by ID
+[**placeOrder**](StoreApi.md#placeorder) | **POST** /store/order | Place an order for a pet
 
 
 # **deleteOrder**
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/UserApi.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/UserApi.md
index c939d874a99..b3b11fe6748 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/UserApi.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib/doc/UserApi.md
@@ -9,14 +9,14 @@ All URIs are relative to *http://petstore.swagger.io/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**createUser**](UserApi.md#createuser) | **post** /user | Create user
-[**createUsersWithArrayInput**](UserApi.md#createuserswitharrayinput) | **post** /user/createWithArray | Creates list of users with given input array
-[**createUsersWithListInput**](UserApi.md#createuserswithlistinput) | **post** /user/createWithList | Creates list of users with given input array
-[**deleteUser**](UserApi.md#deleteuser) | **delete** /user/{username} | Delete user
-[**getUserByName**](UserApi.md#getuserbyname) | **get** /user/{username} | Get user by user name
-[**loginUser**](UserApi.md#loginuser) | **get** /user/login | Logs user into the system
-[**logoutUser**](UserApi.md#logoutuser) | **get** /user/logout | Logs out current logged in user session
-[**updateUser**](UserApi.md#updateuser) | **put** /user/{username} | Updated user
+[**createUser**](UserApi.md#createuser) | **POST** /user | Create user
+[**createUsersWithArrayInput**](UserApi.md#createuserswitharrayinput) | **POST** /user/createWithArray | Creates list of users with given input array
+[**createUsersWithListInput**](UserApi.md#createuserswithlistinput) | **POST** /user/createWithList | Creates list of users with given input array
+[**deleteUser**](UserApi.md#deleteuser) | **DELETE** /user/{username} | Delete user
+[**getUserByName**](UserApi.md#getuserbyname) | **GET** /user/{username} | Get user by user name
+[**loginUser**](UserApi.md#loginuser) | **GET** /user/login | Logs user into the system
+[**logoutUser**](UserApi.md#logoutuser) | **GET** /user/logout | Logs out current logged in user session
+[**updateUser**](UserApi.md#updateuser) | **PUT** /user/{username} | Updated user
 
 
 # **createUser**
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 9b378a4b3fa..70fc2b2dbe6 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
@@ -51,10 +51,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-        'application/xml',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -119,9 +116,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -169,9 +164,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -234,9 +227,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -298,9 +289,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -360,10 +349,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-        'application/xml',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -428,9 +414,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/x-www-form-urlencoded',
-      ].first,
+      contentType: 'application/x-www-form-urlencoded',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -482,9 +466,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'multipart/form-data',
-      ].first,
+      contentType: 'multipart/form-data',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
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 d0184f6eda8..80b074645c8 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
@@ -43,9 +43,7 @@ class StoreApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -91,9 +89,7 @@ class StoreApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -148,9 +144,7 @@ class StoreApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -205,9 +199,7 @@ class StoreApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
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 5253ac66028..fef22be0b97 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
@@ -50,9 +50,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -102,9 +100,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -154,9 +150,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -206,9 +200,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -248,9 +240,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -310,9 +300,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -369,9 +357,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -419,9 +405,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/README.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/README.md
index af00b20ee1d..22789ae7761 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/README.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/README.md
@@ -58,46 +58,46 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Class | Method | HTTP request | Description
 ------------ | ------------- | ------------- | -------------
-*AnotherFakeApi* | [**call123testSpecialTags**](doc/AnotherFakeApi.md#call123testspecialtags) | **patch** /another-fake/dummy | To test special tags
-*DefaultApi* | [**fooGet**](doc/DefaultApi.md#fooget) | **get** /foo | 
-*FakeApi* | [**fakeHealthGet**](doc/FakeApi.md#fakehealthget) | **get** /fake/health | Health check endpoint
-*FakeApi* | [**fakeHttpSignatureTest**](doc/FakeApi.md#fakehttpsignaturetest) | **get** /fake/http-signature-test | test http signature authentication
-*FakeApi* | [**fakeOuterBooleanSerialize**](doc/FakeApi.md#fakeouterbooleanserialize) | **post** /fake/outer/boolean | 
-*FakeApi* | [**fakeOuterCompositeSerialize**](doc/FakeApi.md#fakeoutercompositeserialize) | **post** /fake/outer/composite | 
-*FakeApi* | [**fakeOuterNumberSerialize**](doc/FakeApi.md#fakeouternumberserialize) | **post** /fake/outer/number | 
-*FakeApi* | [**fakeOuterStringSerialize**](doc/FakeApi.md#fakeouterstringserialize) | **post** /fake/outer/string | 
-*FakeApi* | [**fakePropertyEnumIntegerSerialize**](doc/FakeApi.md#fakepropertyenumintegerserialize) | **post** /fake/property/enum-int | 
-*FakeApi* | [**testBodyWithFileSchema**](doc/FakeApi.md#testbodywithfileschema) | **put** /fake/body-with-file-schema | 
-*FakeApi* | [**testBodyWithQueryParams**](doc/FakeApi.md#testbodywithqueryparams) | **put** /fake/body-with-query-params | 
-*FakeApi* | [**testClientModel**](doc/FakeApi.md#testclientmodel) | **patch** /fake | To test \&quot;client\&quot; model
-*FakeApi* | [**testEndpointParameters**](doc/FakeApi.md#testendpointparameters) | **post** /fake | Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트 
-*FakeApi* | [**testEnumParameters**](doc/FakeApi.md#testenumparameters) | **get** /fake | To test enum parameters
-*FakeApi* | [**testGroupParameters**](doc/FakeApi.md#testgroupparameters) | **delete** /fake | Fake endpoint to test group parameters (optional)
-*FakeApi* | [**testInlineAdditionalProperties**](doc/FakeApi.md#testinlineadditionalproperties) | **post** /fake/inline-additionalProperties | test inline additionalProperties
-*FakeApi* | [**testJsonFormData**](doc/FakeApi.md#testjsonformdata) | **get** /fake/jsonFormData | test json serialization of form data
-*FakeApi* | [**testQueryParameterCollectionFormat**](doc/FakeApi.md#testqueryparametercollectionformat) | **put** /fake/test-query-paramters | 
-*FakeClassnameTags123Api* | [**testClassname**](doc/FakeClassnameTags123Api.md#testclassname) | **patch** /fake_classname_test | To test class name in snake case
-*PetApi* | [**addPet**](doc/PetApi.md#addpet) | **post** /pet | Add a new pet to the store
-*PetApi* | [**deletePet**](doc/PetApi.md#deletepet) | **delete** /pet/{petId} | Deletes a pet
-*PetApi* | [**findPetsByStatus**](doc/PetApi.md#findpetsbystatus) | **get** /pet/findByStatus | Finds Pets by status
-*PetApi* | [**findPetsByTags**](doc/PetApi.md#findpetsbytags) | **get** /pet/findByTags | Finds Pets by tags
-*PetApi* | [**getPetById**](doc/PetApi.md#getpetbyid) | **get** /pet/{petId} | Find pet by ID
-*PetApi* | [**updatePet**](doc/PetApi.md#updatepet) | **put** /pet | Update an existing pet
-*PetApi* | [**updatePetWithForm**](doc/PetApi.md#updatepetwithform) | **post** /pet/{petId} | Updates a pet in the store with form data
-*PetApi* | [**uploadFile**](doc/PetApi.md#uploadfile) | **post** /pet/{petId}/uploadImage | uploads an image
-*PetApi* | [**uploadFileWithRequiredFile**](doc/PetApi.md#uploadfilewithrequiredfile) | **post** /fake/{petId}/uploadImageWithRequiredFile | uploads an image (required)
-*StoreApi* | [**deleteOrder**](doc/StoreApi.md#deleteorder) | **delete** /store/order/{order_id} | Delete purchase order by ID
-*StoreApi* | [**getInventory**](doc/StoreApi.md#getinventory) | **get** /store/inventory | Returns pet inventories by status
-*StoreApi* | [**getOrderById**](doc/StoreApi.md#getorderbyid) | **get** /store/order/{order_id} | Find purchase order by ID
-*StoreApi* | [**placeOrder**](doc/StoreApi.md#placeorder) | **post** /store/order | Place an order for a pet
-*UserApi* | [**createUser**](doc/UserApi.md#createuser) | **post** /user | Create user
-*UserApi* | [**createUsersWithArrayInput**](doc/UserApi.md#createuserswitharrayinput) | **post** /user/createWithArray | Creates list of users with given input array
-*UserApi* | [**createUsersWithListInput**](doc/UserApi.md#createuserswithlistinput) | **post** /user/createWithList | Creates list of users with given input array
-*UserApi* | [**deleteUser**](doc/UserApi.md#deleteuser) | **delete** /user/{username} | Delete user
-*UserApi* | [**getUserByName**](doc/UserApi.md#getuserbyname) | **get** /user/{username} | Get user by user name
-*UserApi* | [**loginUser**](doc/UserApi.md#loginuser) | **get** /user/login | Logs user into the system
-*UserApi* | [**logoutUser**](doc/UserApi.md#logoutuser) | **get** /user/logout | Logs out current logged in user session
-*UserApi* | [**updateUser**](doc/UserApi.md#updateuser) | **put** /user/{username} | Updated user
+*AnotherFakeApi* | [**call123testSpecialTags**](doc/AnotherFakeApi.md#call123testspecialtags) | **PATCH** /another-fake/dummy | To test special tags
+*DefaultApi* | [**fooGet**](doc/DefaultApi.md#fooget) | **GET** /foo | 
+*FakeApi* | [**fakeHealthGet**](doc/FakeApi.md#fakehealthget) | **GET** /fake/health | Health check endpoint
+*FakeApi* | [**fakeHttpSignatureTest**](doc/FakeApi.md#fakehttpsignaturetest) | **GET** /fake/http-signature-test | test http signature authentication
+*FakeApi* | [**fakeOuterBooleanSerialize**](doc/FakeApi.md#fakeouterbooleanserialize) | **POST** /fake/outer/boolean | 
+*FakeApi* | [**fakeOuterCompositeSerialize**](doc/FakeApi.md#fakeoutercompositeserialize) | **POST** /fake/outer/composite | 
+*FakeApi* | [**fakeOuterNumberSerialize**](doc/FakeApi.md#fakeouternumberserialize) | **POST** /fake/outer/number | 
+*FakeApi* | [**fakeOuterStringSerialize**](doc/FakeApi.md#fakeouterstringserialize) | **POST** /fake/outer/string | 
+*FakeApi* | [**fakePropertyEnumIntegerSerialize**](doc/FakeApi.md#fakepropertyenumintegerserialize) | **POST** /fake/property/enum-int | 
+*FakeApi* | [**testBodyWithFileSchema**](doc/FakeApi.md#testbodywithfileschema) | **PUT** /fake/body-with-file-schema | 
+*FakeApi* | [**testBodyWithQueryParams**](doc/FakeApi.md#testbodywithqueryparams) | **PUT** /fake/body-with-query-params | 
+*FakeApi* | [**testClientModel**](doc/FakeApi.md#testclientmodel) | **PATCH** /fake | To test \&quot;client\&quot; model
+*FakeApi* | [**testEndpointParameters**](doc/FakeApi.md#testendpointparameters) | **POST** /fake | Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트 
+*FakeApi* | [**testEnumParameters**](doc/FakeApi.md#testenumparameters) | **GET** /fake | To test enum parameters
+*FakeApi* | [**testGroupParameters**](doc/FakeApi.md#testgroupparameters) | **DELETE** /fake | Fake endpoint to test group parameters (optional)
+*FakeApi* | [**testInlineAdditionalProperties**](doc/FakeApi.md#testinlineadditionalproperties) | **POST** /fake/inline-additionalProperties | test inline additionalProperties
+*FakeApi* | [**testJsonFormData**](doc/FakeApi.md#testjsonformdata) | **GET** /fake/jsonFormData | test json serialization of form data
+*FakeApi* | [**testQueryParameterCollectionFormat**](doc/FakeApi.md#testqueryparametercollectionformat) | **PUT** /fake/test-query-paramters | 
+*FakeClassnameTags123Api* | [**testClassname**](doc/FakeClassnameTags123Api.md#testclassname) | **PATCH** /fake_classname_test | To test class name in snake case
+*PetApi* | [**addPet**](doc/PetApi.md#addpet) | **POST** /pet | Add a new pet to the store
+*PetApi* | [**deletePet**](doc/PetApi.md#deletepet) | **DELETE** /pet/{petId} | Deletes a pet
+*PetApi* | [**findPetsByStatus**](doc/PetApi.md#findpetsbystatus) | **GET** /pet/findByStatus | Finds Pets by status
+*PetApi* | [**findPetsByTags**](doc/PetApi.md#findpetsbytags) | **GET** /pet/findByTags | Finds Pets by tags
+*PetApi* | [**getPetById**](doc/PetApi.md#getpetbyid) | **GET** /pet/{petId} | Find pet by ID
+*PetApi* | [**updatePet**](doc/PetApi.md#updatepet) | **PUT** /pet | Update an existing pet
+*PetApi* | [**updatePetWithForm**](doc/PetApi.md#updatepetwithform) | **POST** /pet/{petId} | Updates a pet in the store with form data
+*PetApi* | [**uploadFile**](doc/PetApi.md#uploadfile) | **POST** /pet/{petId}/uploadImage | uploads an image
+*PetApi* | [**uploadFileWithRequiredFile**](doc/PetApi.md#uploadfilewithrequiredfile) | **POST** /fake/{petId}/uploadImageWithRequiredFile | uploads an image (required)
+*StoreApi* | [**deleteOrder**](doc/StoreApi.md#deleteorder) | **DELETE** /store/order/{order_id} | Delete purchase order by ID
+*StoreApi* | [**getInventory**](doc/StoreApi.md#getinventory) | **GET** /store/inventory | Returns pet inventories by status
+*StoreApi* | [**getOrderById**](doc/StoreApi.md#getorderbyid) | **GET** /store/order/{order_id} | Find purchase order by ID
+*StoreApi* | [**placeOrder**](doc/StoreApi.md#placeorder) | **POST** /store/order | Place an order for a pet
+*UserApi* | [**createUser**](doc/UserApi.md#createuser) | **POST** /user | Create user
+*UserApi* | [**createUsersWithArrayInput**](doc/UserApi.md#createuserswitharrayinput) | **POST** /user/createWithArray | Creates list of users with given input array
+*UserApi* | [**createUsersWithListInput**](doc/UserApi.md#createuserswithlistinput) | **POST** /user/createWithList | Creates list of users with given input array
+*UserApi* | [**deleteUser**](doc/UserApi.md#deleteuser) | **DELETE** /user/{username} | Delete user
+*UserApi* | [**getUserByName**](doc/UserApi.md#getuserbyname) | **GET** /user/{username} | Get user by user name
+*UserApi* | [**loginUser**](doc/UserApi.md#loginuser) | **GET** /user/login | Logs user into the system
+*UserApi* | [**logoutUser**](doc/UserApi.md#logoutuser) | **GET** /user/logout | Logs out current logged in user session
+*UserApi* | [**updateUser**](doc/UserApi.md#updateuser) | **PUT** /user/{username} | Updated user
 
 
 ## Documentation For Models
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/AnotherFakeApi.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/AnotherFakeApi.md
index d55663297c1..bb401f7c20c 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/AnotherFakeApi.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/AnotherFakeApi.md
@@ -9,7 +9,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**call123testSpecialTags**](AnotherFakeApi.md#call123testspecialtags) | **patch** /another-fake/dummy | To test special tags
+[**call123testSpecialTags**](AnotherFakeApi.md#call123testspecialtags) | **PATCH** /another-fake/dummy | To test special tags
 
 
 # **call123testSpecialTags**
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/DefaultApi.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/DefaultApi.md
index be916c3037d..5c305ecaa71 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/DefaultApi.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/DefaultApi.md
@@ -9,7 +9,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**fooGet**](DefaultApi.md#fooget) | **get** /foo | 
+[**fooGet**](DefaultApi.md#fooget) | **GET** /foo | 
 
 
 # **fooGet**
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/FakeApi.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/FakeApi.md
index 41ab4e4fc12..b28fe4abbe3 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/FakeApi.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/FakeApi.md
@@ -9,22 +9,22 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**fakeHealthGet**](FakeApi.md#fakehealthget) | **get** /fake/health | Health check endpoint
-[**fakeHttpSignatureTest**](FakeApi.md#fakehttpsignaturetest) | **get** /fake/http-signature-test | test http signature authentication
-[**fakeOuterBooleanSerialize**](FakeApi.md#fakeouterbooleanserialize) | **post** /fake/outer/boolean | 
-[**fakeOuterCompositeSerialize**](FakeApi.md#fakeoutercompositeserialize) | **post** /fake/outer/composite | 
-[**fakeOuterNumberSerialize**](FakeApi.md#fakeouternumberserialize) | **post** /fake/outer/number | 
-[**fakeOuterStringSerialize**](FakeApi.md#fakeouterstringserialize) | **post** /fake/outer/string | 
-[**fakePropertyEnumIntegerSerialize**](FakeApi.md#fakepropertyenumintegerserialize) | **post** /fake/property/enum-int | 
-[**testBodyWithFileSchema**](FakeApi.md#testbodywithfileschema) | **put** /fake/body-with-file-schema | 
-[**testBodyWithQueryParams**](FakeApi.md#testbodywithqueryparams) | **put** /fake/body-with-query-params | 
-[**testClientModel**](FakeApi.md#testclientmodel) | **patch** /fake | To test \&quot;client\&quot; model
-[**testEndpointParameters**](FakeApi.md#testendpointparameters) | **post** /fake | Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트 
-[**testEnumParameters**](FakeApi.md#testenumparameters) | **get** /fake | To test enum parameters
-[**testGroupParameters**](FakeApi.md#testgroupparameters) | **delete** /fake | Fake endpoint to test group parameters (optional)
-[**testInlineAdditionalProperties**](FakeApi.md#testinlineadditionalproperties) | **post** /fake/inline-additionalProperties | test inline additionalProperties
-[**testJsonFormData**](FakeApi.md#testjsonformdata) | **get** /fake/jsonFormData | test json serialization of form data
-[**testQueryParameterCollectionFormat**](FakeApi.md#testqueryparametercollectionformat) | **put** /fake/test-query-paramters | 
+[**fakeHealthGet**](FakeApi.md#fakehealthget) | **GET** /fake/health | Health check endpoint
+[**fakeHttpSignatureTest**](FakeApi.md#fakehttpsignaturetest) | **GET** /fake/http-signature-test | test http signature authentication
+[**fakeOuterBooleanSerialize**](FakeApi.md#fakeouterbooleanserialize) | **POST** /fake/outer/boolean | 
+[**fakeOuterCompositeSerialize**](FakeApi.md#fakeoutercompositeserialize) | **POST** /fake/outer/composite | 
+[**fakeOuterNumberSerialize**](FakeApi.md#fakeouternumberserialize) | **POST** /fake/outer/number | 
+[**fakeOuterStringSerialize**](FakeApi.md#fakeouterstringserialize) | **POST** /fake/outer/string | 
+[**fakePropertyEnumIntegerSerialize**](FakeApi.md#fakepropertyenumintegerserialize) | **POST** /fake/property/enum-int | 
+[**testBodyWithFileSchema**](FakeApi.md#testbodywithfileschema) | **PUT** /fake/body-with-file-schema | 
+[**testBodyWithQueryParams**](FakeApi.md#testbodywithqueryparams) | **PUT** /fake/body-with-query-params | 
+[**testClientModel**](FakeApi.md#testclientmodel) | **PATCH** /fake | To test \&quot;client\&quot; model
+[**testEndpointParameters**](FakeApi.md#testendpointparameters) | **POST** /fake | Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트 
+[**testEnumParameters**](FakeApi.md#testenumparameters) | **GET** /fake | To test enum parameters
+[**testGroupParameters**](FakeApi.md#testgroupparameters) | **DELETE** /fake | Fake endpoint to test group parameters (optional)
+[**testInlineAdditionalProperties**](FakeApi.md#testinlineadditionalproperties) | **POST** /fake/inline-additionalProperties | test inline additionalProperties
+[**testJsonFormData**](FakeApi.md#testjsonformdata) | **GET** /fake/jsonFormData | test json serialization of form data
+[**testQueryParameterCollectionFormat**](FakeApi.md#testqueryparametercollectionformat) | **PUT** /fake/test-query-paramters | 
 
 
 # **fakeHealthGet**
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/FakeClassnameTags123Api.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/FakeClassnameTags123Api.md
index 9745ca8e3ff..98fe0b47358 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/FakeClassnameTags123Api.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/FakeClassnameTags123Api.md
@@ -9,7 +9,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**testClassname**](FakeClassnameTags123Api.md#testclassname) | **patch** /fake_classname_test | To test class name in snake case
+[**testClassname**](FakeClassnameTags123Api.md#testclassname) | **PATCH** /fake_classname_test | To test class name in snake case
 
 
 # **testClassname**
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/PetApi.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/PetApi.md
index d5a07d5046e..841eed63291 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/PetApi.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/PetApi.md
@@ -9,15 +9,15 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**addPet**](PetApi.md#addpet) | **post** /pet | Add a new pet to the store
-[**deletePet**](PetApi.md#deletepet) | **delete** /pet/{petId} | Deletes a pet
-[**findPetsByStatus**](PetApi.md#findpetsbystatus) | **get** /pet/findByStatus | Finds Pets by status
-[**findPetsByTags**](PetApi.md#findpetsbytags) | **get** /pet/findByTags | Finds Pets by tags
-[**getPetById**](PetApi.md#getpetbyid) | **get** /pet/{petId} | Find pet by ID
-[**updatePet**](PetApi.md#updatepet) | **put** /pet | Update an existing pet
-[**updatePetWithForm**](PetApi.md#updatepetwithform) | **post** /pet/{petId} | Updates a pet in the store with form data
-[**uploadFile**](PetApi.md#uploadfile) | **post** /pet/{petId}/uploadImage | uploads an image
-[**uploadFileWithRequiredFile**](PetApi.md#uploadfilewithrequiredfile) | **post** /fake/{petId}/uploadImageWithRequiredFile | uploads an image (required)
+[**addPet**](PetApi.md#addpet) | **POST** /pet | Add a new pet to the store
+[**deletePet**](PetApi.md#deletepet) | **DELETE** /pet/{petId} | Deletes a pet
+[**findPetsByStatus**](PetApi.md#findpetsbystatus) | **GET** /pet/findByStatus | Finds Pets by status
+[**findPetsByTags**](PetApi.md#findpetsbytags) | **GET** /pet/findByTags | Finds Pets by tags
+[**getPetById**](PetApi.md#getpetbyid) | **GET** /pet/{petId} | Find pet by ID
+[**updatePet**](PetApi.md#updatepet) | **PUT** /pet | Update an existing pet
+[**updatePetWithForm**](PetApi.md#updatepetwithform) | **POST** /pet/{petId} | Updates a pet in the store with form data
+[**uploadFile**](PetApi.md#uploadfile) | **POST** /pet/{petId}/uploadImage | uploads an image
+[**uploadFileWithRequiredFile**](PetApi.md#uploadfilewithrequiredfile) | **POST** /fake/{petId}/uploadImageWithRequiredFile | uploads an image (required)
 
 
 # **addPet**
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/StoreApi.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/StoreApi.md
index 1fcb8f71eea..a7dbf9ad019 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/StoreApi.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/StoreApi.md
@@ -9,10 +9,10 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**deleteOrder**](StoreApi.md#deleteorder) | **delete** /store/order/{order_id} | Delete purchase order by ID
-[**getInventory**](StoreApi.md#getinventory) | **get** /store/inventory | Returns pet inventories by status
-[**getOrderById**](StoreApi.md#getorderbyid) | **get** /store/order/{order_id} | Find purchase order by ID
-[**placeOrder**](StoreApi.md#placeorder) | **post** /store/order | Place an order for a pet
+[**deleteOrder**](StoreApi.md#deleteorder) | **DELETE** /store/order/{order_id} | Delete purchase order by ID
+[**getInventory**](StoreApi.md#getinventory) | **GET** /store/inventory | Returns pet inventories by status
+[**getOrderById**](StoreApi.md#getorderbyid) | **GET** /store/order/{order_id} | Find purchase order by ID
+[**placeOrder**](StoreApi.md#placeorder) | **POST** /store/order | Place an order for a pet
 
 
 # **deleteOrder**
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/UserApi.md b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/UserApi.md
index 62e01652e80..32bc2e675da 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/UserApi.md
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/doc/UserApi.md
@@ -9,14 +9,14 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 
 Method | HTTP request | Description
 ------------- | ------------- | -------------
-[**createUser**](UserApi.md#createuser) | **post** /user | Create user
-[**createUsersWithArrayInput**](UserApi.md#createuserswitharrayinput) | **post** /user/createWithArray | Creates list of users with given input array
-[**createUsersWithListInput**](UserApi.md#createuserswithlistinput) | **post** /user/createWithList | Creates list of users with given input array
-[**deleteUser**](UserApi.md#deleteuser) | **delete** /user/{username} | Delete user
-[**getUserByName**](UserApi.md#getuserbyname) | **get** /user/{username} | Get user by user name
-[**loginUser**](UserApi.md#loginuser) | **get** /user/login | Logs user into the system
-[**logoutUser**](UserApi.md#logoutuser) | **get** /user/logout | Logs out current logged in user session
-[**updateUser**](UserApi.md#updateuser) | **put** /user/{username} | Updated user
+[**createUser**](UserApi.md#createuser) | **POST** /user | Create user
+[**createUsersWithArrayInput**](UserApi.md#createuserswitharrayinput) | **POST** /user/createWithArray | Creates list of users with given input array
+[**createUsersWithListInput**](UserApi.md#createuserswithlistinput) | **POST** /user/createWithList | Creates list of users with given input array
+[**deleteUser**](UserApi.md#deleteuser) | **DELETE** /user/{username} | Delete user
+[**getUserByName**](UserApi.md#getuserbyname) | **GET** /user/{username} | Get user by user name
+[**loginUser**](UserApi.md#loginuser) | **GET** /user/login | Logs user into the system
+[**logoutUser**](UserApi.md#logoutuser) | **GET** /user/logout | Logs out current logged in user session
+[**updateUser**](UserApi.md#updateuser) | **PUT** /user/{username} | Updated user
 
 
 # **createUser**
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 4bea8f87dbd..cabc80b7798 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
@@ -42,9 +42,7 @@ class AnotherFakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
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 ab47f0a6571..51dd7ea125e 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
@@ -41,9 +41,7 @@ class DefaultApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
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 b50d02d5cf6..a8310d5f4a2 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
@@ -50,9 +50,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -118,10 +116,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-        'application/xml',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -164,9 +159,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -219,9 +212,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -279,9 +270,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -334,9 +323,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -389,9 +376,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -449,9 +434,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -498,9 +481,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -543,9 +524,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -621,9 +600,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/x-www-form-urlencoded',
-      ].first,
+      contentType: 'application/x-www-form-urlencoded',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -695,9 +672,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/x-www-form-urlencoded',
-      ].first,
+      contentType: 'application/x-www-form-urlencoded',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -760,9 +735,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -802,9 +775,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -848,9 +819,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/x-www-form-urlencoded',
-      ].first,
+      contentType: 'application/x-www-form-urlencoded',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -906,9 +875,7 @@ class FakeApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
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 f9b44deb6d5..54c40f0e343 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
@@ -49,9 +49,7 @@ class FakeClassnameTags123Api {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
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 56bdd8556bc..9cc7beeb57e 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
@@ -51,10 +51,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-        'application/xml',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -104,9 +101,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -154,9 +149,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -219,9 +212,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -283,9 +274,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -345,10 +334,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-        'application/xml',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -398,9 +384,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/x-www-form-urlencoded',
-      ].first,
+      contentType: 'application/x-www-form-urlencoded',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -452,9 +436,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'multipart/form-data',
-      ].first,
+      contentType: 'multipart/form-data',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -521,9 +503,7 @@ class PetApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'multipart/form-data',
-      ].first,
+      contentType: 'multipart/form-data',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
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 e6c7679d1cd..14fa8b60121 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
@@ -43,9 +43,7 @@ class StoreApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -91,9 +89,7 @@ class StoreApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -148,9 +144,7 @@ class StoreApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -205,9 +199,7 @@ class StoreApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
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 d85fbcc8585..86032dba94a 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
@@ -43,9 +43,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -88,9 +86,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -133,9 +129,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -178,9 +172,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -220,9 +212,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -282,9 +272,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -334,9 +322,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,
@@ -377,9 +363,7 @@ class UserApi {
         ...?extra,
       },
       validateStatus: validateStatus,
-      contentType: [
-        'application/json',
-      ].first,
+      contentType: 'application/json',
       cancelToken: cancelToken,
       onSendProgress: onSendProgress,
       onReceiveProgress: onReceiveProgress,