diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-spring-webclient/api.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-spring-webclient/api.mustache
index e4d9c005a63c..84191cfe1bda 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-spring-webclient/api.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-spring-webclient/api.mustache
@@ -72,7 +72,7 @@ import {{packageName}}.infrastructure.*
     {{/isDeprecated}}
     {{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}fun {{operationId}}({{#allParams}}{{{paramName}}}: {{#isEnum}}{{#isContainer}}kotlin.collections.List<{{enumName}}{{operationIdCamelCase}}>{{/isContainer}}{{^isContainer}}{{enumName}}{{operationIdCamelCase}}{{/isContainer}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}{{^required}}?{{#defaultValue}} = {{>param_default_value}}{{/defaultValue}}{{^defaultValue}} = null{{/defaultValue}}{{/required}}{{^-last}}, {{/-last}}{{/allParams}}): Mono<{{#returnType}}{{{returnType}}}{{#nullableReturnType}}?{{/nullableReturnType}}{{/returnType}}{{^returnType}}Unit{{/returnType}}> {
         return {{operationId}}WithHttpInfo({{#allParams}}{{{paramName}}} = {{{paramName}}}{{^-last}}, {{/-last}}{{/allParams}})
-            .map { {{#returnType}}it.body{{/returnType}}{{^returnType}}Unit{{/returnType}} }
+            .map { {{#returnType}}it.body!!{{/returnType}}{{^returnType}}Unit{{/returnType}} }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/AuthApi.kt b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/AuthApi.kt
index 332f06549248..852c800048d3 100644
--- a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/AuthApi.kt
+++ b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/AuthApi.kt
@@ -43,7 +43,7 @@ open class AuthApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testAuthHttpBasic(): Mono<kotlin.String> {
         return testAuthHttpBasicWithHttpInfo()
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -78,7 +78,7 @@ open class AuthApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testAuthHttpBearer(): Mono<kotlin.String> {
         return testAuthHttpBearerWithHttpInfo()
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/BodyApi.kt b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/BodyApi.kt
index 48b26eeb45f4..4e1dbe75de3e 100644
--- a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/BodyApi.kt
+++ b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/BodyApi.kt
@@ -45,7 +45,7 @@ open class BodyApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testBinaryGif(): Mono<java.io.File> {
         return testBinaryGifWithHttpInfo()
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -80,7 +80,7 @@ open class BodyApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testBodyApplicationOctetstreamBinary(body: java.io.File? = null): Mono<kotlin.String> {
         return testBodyApplicationOctetstreamBinaryWithHttpInfo(body = body)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -116,7 +116,7 @@ open class BodyApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testBodyMultipartFormdataArrayOfBinary(files: kotlin.collections.List<java.io.File>): Mono<kotlin.String> {
         return testBodyMultipartFormdataArrayOfBinaryWithHttpInfo(files = files)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -152,7 +152,7 @@ open class BodyApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testBodyMultipartFormdataSingleBinary(myFile: java.io.File? = null): Mono<kotlin.String> {
         return testBodyMultipartFormdataSingleBinaryWithHttpInfo(myFile = myFile)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -188,7 +188,7 @@ open class BodyApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testEchoBodyFreeFormObjectResponseString(body: kotlin.Any? = null): Mono<kotlin.String> {
         return testEchoBodyFreeFormObjectResponseStringWithHttpInfo(body = body)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -224,7 +224,7 @@ open class BodyApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testEchoBodyPet(pet: Pet? = null): Mono<Pet> {
         return testEchoBodyPetWithHttpInfo(pet = pet)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -260,7 +260,7 @@ open class BodyApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testEchoBodyPetResponseString(pet: Pet? = null): Mono<kotlin.String> {
         return testEchoBodyPetResponseStringWithHttpInfo(pet = pet)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -296,7 +296,7 @@ open class BodyApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testEchoBodyTagResponseString(tag: Tag? = null): Mono<kotlin.String> {
         return testEchoBodyTagResponseStringWithHttpInfo(tag = tag)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/FormApi.kt b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/FormApi.kt
index bed8a675e994..e9dec9440a10 100644
--- a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/FormApi.kt
+++ b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/FormApi.kt
@@ -43,7 +43,7 @@ open class FormApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testFormIntegerBooleanString(integerForm: kotlin.Int? = null, booleanForm: kotlin.Boolean? = null, stringForm: kotlin.String? = null): Mono<kotlin.String> {
         return testFormIntegerBooleanStringWithHttpInfo(integerForm = integerForm, booleanForm = booleanForm, stringForm = stringForm)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -81,7 +81,7 @@ open class FormApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testFormOneof(form1: kotlin.String? = null, form2: kotlin.Int? = null, form3: kotlin.String? = null, form4: kotlin.Boolean? = null, id: kotlin.Long? = null, name: kotlin.String? = null): Mono<kotlin.String> {
         return testFormOneofWithHttpInfo(form1 = form1, form2 = form2, form3 = form3, form4 = form4, id = id, name = name)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/HeaderApi.kt b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/HeaderApi.kt
index 84348888eb5a..f5bef07b6a6d 100644
--- a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/HeaderApi.kt
+++ b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/HeaderApi.kt
@@ -53,7 +53,7 @@ open class HeaderApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testHeaderIntegerBooleanStringEnums(integerHeader: kotlin.Int? = null, booleanHeader: kotlin.Boolean? = null, stringHeader: kotlin.String? = null, enumNonrefStringHeader: EnumNonrefStringHeaderTestHeaderIntegerBooleanStringEnums? = null, enumRefStringHeader: StringEnumRef? = null): Mono<kotlin.String> {
         return testHeaderIntegerBooleanStringEnumsWithHttpInfo(integerHeader = integerHeader, booleanHeader = booleanHeader, stringHeader = stringHeader, enumNonrefStringHeader = enumNonrefStringHeader, enumRefStringHeader = enumRefStringHeader)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/PathApi.kt b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/PathApi.kt
index ad7dd877ae32..467489f45a62 100644
--- a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/PathApi.kt
+++ b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/PathApi.kt
@@ -53,7 +53,7 @@ open class PathApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testsPathStringPathStringIntegerPathIntegerEnumNonrefStringPathEnumRefStringPath(pathString: kotlin.String, pathInteger: kotlin.Int, enumNonrefStringPath: EnumNonrefStringPathTestsPathStringPathStringIntegerPathIntegerEnumNonrefStringPathEnumRefStringPath, enumRefStringPath: StringEnumRef): Mono<kotlin.String> {
         return testsPathStringPathStringIntegerPathIntegerEnumNonrefStringPathEnumRefStringPathWithHttpInfo(pathString = pathString, pathInteger = pathInteger, enumNonrefStringPath = enumNonrefStringPath, enumRefStringPath = enumRefStringPath)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/QueryApi.kt b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/QueryApi.kt
index e4af8b23528f..c2b3333e3f7e 100644
--- a/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/QueryApi.kt
+++ b/samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/QueryApi.kt
@@ -55,7 +55,7 @@ open class QueryApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testEnumRefString(enumNonrefStringQuery: EnumNonrefStringQueryTestEnumRefString? = null, enumRefStringQuery: StringEnumRef? = null): Mono<kotlin.String> {
         return testEnumRefStringWithHttpInfo(enumNonrefStringQuery = enumNonrefStringQuery, enumRefStringQuery = enumRefStringQuery)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -98,7 +98,7 @@ open class QueryApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testQueryDatetimeDateString(datetimeQuery: java.time.OffsetDateTime? = null, dateQuery: java.time.LocalDate? = null, stringQuery: kotlin.String? = null): Mono<kotlin.String> {
         return testQueryDatetimeDateStringWithHttpInfo(datetimeQuery = datetimeQuery, dateQuery = dateQuery, stringQuery = stringQuery)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -144,7 +144,7 @@ open class QueryApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testQueryIntegerBooleanString(integerQuery: kotlin.Int? = null, booleanQuery: kotlin.Boolean? = null, stringQuery: kotlin.String? = null): Mono<kotlin.String> {
         return testQueryIntegerBooleanStringWithHttpInfo(integerQuery = integerQuery, booleanQuery = booleanQuery, stringQuery = stringQuery)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -190,7 +190,7 @@ open class QueryApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testQueryStyleDeepObjectExplodeTrueObject(queryObject: Pet? = null): Mono<kotlin.String> {
         return testQueryStyleDeepObjectExplodeTrueObjectWithHttpInfo(queryObject = queryObject)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -230,7 +230,7 @@ open class QueryApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testQueryStyleFormExplodeTrueArrayString(queryObject: TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter? = null): Mono<kotlin.String> {
         return testQueryStyleFormExplodeTrueArrayStringWithHttpInfo(queryObject = queryObject)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -270,7 +270,7 @@ open class QueryApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun testQueryStyleFormExplodeTrueObject(queryObject: Pet? = null): Mono<kotlin.String> {
         return testQueryStyleFormExplodeTrueObjectWithHttpInfo(queryObject = queryObject)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/PetApi.kt b/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
index 29149b7d621e..f5c95fb92f94 100644
--- a/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
+++ b/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
@@ -45,7 +45,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun addPet(pet: Pet): Mono<Pet> {
         return addPetWithHttpInfo(pet = pet)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -127,7 +127,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun findPetsByStatus(status: kotlin.collections.List<StatusFindPetsByStatus>): Mono<kotlin.collections.List<Pet>> {
         return findPetsByStatusWithHttpInfo(status = status)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -166,7 +166,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Deprecated(message = "This operation is deprecated.")
     fun findPetsByTags(tags: kotlin.collections.List<kotlin.String>): Mono<kotlin.collections.List<Pet>> {
         return findPetsByTagsWithHttpInfo(tags = tags)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -206,7 +206,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun getPetById(petId: kotlin.Long): Mono<Pet> {
         return getPetByIdWithHttpInfo(petId = petId)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -242,7 +242,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun updatePet(pet: Pet): Mono<Pet> {
         return updatePetWithHttpInfo(pet = pet)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -316,7 +316,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun uploadFile(petId: kotlin.Long, additionalMetadata: kotlin.String? = null, file: java.io.File? = null): Mono<ModelApiResponse> {
         return uploadFileWithHttpInfo(petId = petId, additionalMetadata = additionalMetadata, file = file)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt b/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
index 90063a10c1b4..4559304452ab 100644
--- a/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
+++ b/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
@@ -79,7 +79,7 @@ open class StoreApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun getInventory(): Mono<kotlin.collections.Map<kotlin.String, kotlin.Int>> {
         return getInventoryWithHttpInfo()
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -114,7 +114,7 @@ open class StoreApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun getOrderById(orderId: kotlin.Long): Mono<Order> {
         return getOrderByIdWithHttpInfo(orderId = orderId)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -150,7 +150,7 @@ open class StoreApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun placeOrder(order: Order): Mono<Order> {
         return placeOrderWithHttpInfo(order = order)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/UserApi.kt b/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
index 9a7bdac04626..0593134e68d3 100644
--- a/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
+++ b/samples/client/petstore/kotlin-jvm-spring-2-webclient/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
@@ -184,7 +184,7 @@ open class UserApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun getUserByName(username: kotlin.String): Mono<User> {
         return getUserByNameWithHttpInfo(username = username)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -220,7 +220,7 @@ open class UserApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun loginUser(username: kotlin.String, password: kotlin.String): Mono<kotlin.String> {
         return loginUserWithHttpInfo(username = username, password = password)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/PetApi.kt b/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
index 29149b7d621e..f5c95fb92f94 100644
--- a/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
+++ b/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
@@ -45,7 +45,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun addPet(pet: Pet): Mono<Pet> {
         return addPetWithHttpInfo(pet = pet)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -127,7 +127,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun findPetsByStatus(status: kotlin.collections.List<StatusFindPetsByStatus>): Mono<kotlin.collections.List<Pet>> {
         return findPetsByStatusWithHttpInfo(status = status)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -166,7 +166,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Deprecated(message = "This operation is deprecated.")
     fun findPetsByTags(tags: kotlin.collections.List<kotlin.String>): Mono<kotlin.collections.List<Pet>> {
         return findPetsByTagsWithHttpInfo(tags = tags)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -206,7 +206,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun getPetById(petId: kotlin.Long): Mono<Pet> {
         return getPetByIdWithHttpInfo(petId = petId)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -242,7 +242,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun updatePet(pet: Pet): Mono<Pet> {
         return updatePetWithHttpInfo(pet = pet)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -316,7 +316,7 @@ open class PetApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun uploadFile(petId: kotlin.Long, additionalMetadata: kotlin.String? = null, file: java.io.File? = null): Mono<ModelApiResponse> {
         return uploadFileWithHttpInfo(petId = petId, additionalMetadata = additionalMetadata, file = file)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt b/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
index 90063a10c1b4..4559304452ab 100644
--- a/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
+++ b/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
@@ -79,7 +79,7 @@ open class StoreApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun getInventory(): Mono<kotlin.collections.Map<kotlin.String, kotlin.Int>> {
         return getInventoryWithHttpInfo()
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -114,7 +114,7 @@ open class StoreApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun getOrderById(orderId: kotlin.Long): Mono<Order> {
         return getOrderByIdWithHttpInfo(orderId = orderId)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -150,7 +150,7 @@ open class StoreApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun placeOrder(order: Order): Mono<Order> {
         return placeOrderWithHttpInfo(order = order)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
diff --git a/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/UserApi.kt b/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
index 9a7bdac04626..0593134e68d3 100644
--- a/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
+++ b/samples/client/petstore/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
@@ -184,7 +184,7 @@ open class UserApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun getUserByName(username: kotlin.String): Mono<User> {
         return getUserByNameWithHttpInfo(username = username)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)
@@ -220,7 +220,7 @@ open class UserApi(client: WebClient) : ApiClient(client) {
     @Throws(WebClientResponseException::class)
     fun loginUser(username: kotlin.String, password: kotlin.String): Mono<kotlin.String> {
         return loginUserWithHttpInfo(username = username, password = password)
-            .map { it.body }
+            .map { it.body!! }
     }
 
     @Throws(WebClientResponseException::class)