diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractKotlinCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractKotlinCodegen.java
index aa4015303392..bc582f756160 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractKotlinCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractKotlinCodegen.java
@@ -940,7 +940,7 @@ public String toDefaultValue(Schema p) {
             }
         } else if (ModelUtils.isStringSchema(p)) {
             if (p.getDefault() != null) {
-                return "'" + p.getDefault() + "'";
+                return "\"" + p.getDefault() + "\"";
             }
         }
 
diff --git a/samples/server/petstore/kotlin-springboot-modelMutable/.openapi-generator/VERSION b/samples/server/petstore/kotlin-springboot-modelMutable/.openapi-generator/VERSION
index 58592f031f65..b5d898602c2c 100644
--- a/samples/server/petstore/kotlin-springboot-modelMutable/.openapi-generator/VERSION
+++ b/samples/server/petstore/kotlin-springboot-modelMutable/.openapi-generator/VERSION
@@ -1 +1 @@
-4.2.3-SNAPSHOT
\ No newline at end of file
+4.3.1-SNAPSHOT
\ No newline at end of file
diff --git a/samples/server/petstore/kotlin-springboot-modelMutable/build.gradle.kts b/samples/server/petstore/kotlin-springboot-modelMutable/build.gradle.kts
index 26f4601e5705..49fe9400f70d 100644
--- a/samples/server/petstore/kotlin-springboot-modelMutable/build.gradle.kts
+++ b/samples/server/petstore/kotlin-springboot-modelMutable/build.gradle.kts
@@ -3,7 +3,7 @@ import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 buildscript {
     repositories {
         jcenter()
-        mavenCentral()
+        maven { url = uri("https://repo1.maven.org/maven2") }
     }
     dependencies {
         classpath("org.springframework.boot:spring-boot-gradle-plugin:2.2.0.M3")
@@ -15,7 +15,7 @@ version = "1.0.0"
 
 repositories {
     jcenter()
-    mavenCentral()
+    maven { url = uri("https://repo1.maven.org/maven2") }
 }
 
 tasks.withType<KotlinCompile> {
@@ -48,7 +48,7 @@ dependencies {
 }
 
 repositories {
-	mavenCentral()
+	maven { url = uri("https://repo1.maven.org/maven2") }
 	maven { url = uri("https://repo.spring.io/snapshot") }
 	maven { url = uri("https://repo.spring.io/milestone") }
 }
diff --git a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/api/ApiUtil.kt b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/api/ApiUtil.kt
new file mode 100644
index 000000000000..958a6f3ebfe8
--- /dev/null
+++ b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/api/ApiUtil.kt
@@ -0,0 +1,19 @@
+package org.openapitools.api
+
+import org.springframework.web.context.request.NativeWebRequest
+
+import javax.servlet.http.HttpServletResponse
+import java.io.IOException
+
+object ApiUtil {
+    fun setExampleResponse(req: NativeWebRequest, contentType: String, example: String) {
+        try {
+            val res = req.getNativeResponse(HttpServletResponse::class.java)
+            res.setCharacterEncoding("UTF-8")
+            res.addHeader("Content-Type", contentType)
+            res.getWriter().print(example)
+        } catch (e: IOException) {
+            throw RuntimeException(e)
+        }
+    }
+}
diff --git a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/api/Exceptions.kt b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/api/Exceptions.kt
index 4d8400902aa9..44190af7a019 100644
--- a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/api/Exceptions.kt
+++ b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/api/Exceptions.kt
@@ -17,13 +17,13 @@ class DefaultExceptionHandler {
 
     @ExceptionHandler(value = [ApiException::class])
     fun onApiException(ex: ApiException, response: HttpServletResponse): Unit =
-            response.sendError(ex.code, ex.message)
+        response.sendError(ex.code, ex.message)
 
     @ExceptionHandler(value = [NotImplementedError::class])
     fun onNotImplemented(ex: NotImplementedError, response: HttpServletResponse): Unit =
-            response.sendError(HttpStatus.NOT_IMPLEMENTED.value())
+        response.sendError(HttpStatus.NOT_IMPLEMENTED.value())
 
     @ExceptionHandler(value = [ConstraintViolationException::class])
     fun onConstraintViolation(ex: ConstraintViolationException, response: HttpServletResponse): Unit =
-            response.sendError(HttpStatus.BAD_REQUEST.value(), ex.constraintViolations.joinToString(", ") { it.message })
+        response.sendError(HttpStatus.BAD_REQUEST.value(), ex.constraintViolations.joinToString(", ") { it.message })
 }
diff --git a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Category.kt b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Category.kt
index 74e95802723e..bc0b66d8aba2 100644
--- a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Category.kt
+++ b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Category.kt
@@ -16,13 +16,13 @@ import io.swagger.annotations.ApiModelProperty
  * @param id 
  * @param name 
  */
-data class Category (
+data class Category(
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("id") var id: kotlin.Long? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("id") var id: kotlin.Long? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("name") var name: kotlin.String? = null
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("name") var name: kotlin.String? = null
 ) {
 
 }
diff --git a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/ModelApiResponse.kt b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/ModelApiResponse.kt
index a121d4abe1d1..a73c2bacacef 100644
--- a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/ModelApiResponse.kt
+++ b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/ModelApiResponse.kt
@@ -17,16 +17,16 @@ import io.swagger.annotations.ApiModelProperty
  * @param type 
  * @param message 
  */
-data class ModelApiResponse (
+data class ModelApiResponse(
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("code") var code: kotlin.Int? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("code") var code: kotlin.Int? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("type") var type: kotlin.String? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("type") var type: kotlin.String? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("message") var message: kotlin.String? = null
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("message") var message: kotlin.String? = null
 ) {
 
 }
diff --git a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Order.kt b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Order.kt
index 5ed9ea534974..474fd5a82b2d 100644
--- a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Order.kt
+++ b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Order.kt
@@ -21,25 +21,25 @@ import io.swagger.annotations.ApiModelProperty
  * @param status Order Status
  * @param complete 
  */
-data class Order (
+data class Order(
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("id") var id: kotlin.Long? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("id") var id: kotlin.Long? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("petId") var petId: kotlin.Long? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("petId") var petId: kotlin.Long? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("quantity") var quantity: kotlin.Int? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("quantity") var quantity: kotlin.Int? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("shipDate") var shipDate: java.time.OffsetDateTime? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("shipDate") var shipDate: java.time.OffsetDateTime? = null,
 
-        @ApiModelProperty(example = "null", value = "Order Status")
-        @JsonProperty("status") var status: Order.Status? = null,
+    @ApiModelProperty(example = "null", value = "Order Status")
+    @JsonProperty("status") var status: Order.Status? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("complete") var complete: kotlin.Boolean? = null
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("complete") var complete: kotlin.Boolean? = null
 ) {
 
     /**
diff --git a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Pet.kt b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Pet.kt
index 5868cb23e3ff..7386590e96cf 100644
--- a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Pet.kt
+++ b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Pet.kt
@@ -23,27 +23,27 @@ import io.swagger.annotations.ApiModelProperty
  * @param tags 
  * @param status pet status in the store
  */
-data class Pet (
+data class Pet(
 
-        @get:NotNull 
-        @ApiModelProperty(example = "doggie", required = true, value = "")
-        @JsonProperty("name") var name: kotlin.String,
+    @get:NotNull 
+    @ApiModelProperty(example = "doggie", required = true, value = "")
+    @JsonProperty("name") var name: kotlin.String,
 
-        @get:NotNull 
-        @ApiModelProperty(example = "null", required = true, value = "")
-        @JsonProperty("photoUrls") var photoUrls: kotlin.collections.List<kotlin.String>,
+    @get:NotNull 
+    @ApiModelProperty(example = "null", required = true, value = "")
+    @JsonProperty("photoUrls") var photoUrls: kotlin.collections.List<kotlin.String>,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("id") var id: kotlin.Long? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("id") var id: kotlin.Long? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("category") var category: Category? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("category") var category: Category? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("tags") var tags: kotlin.collections.List<Tag>? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("tags") var tags: kotlin.collections.List<Tag>? = null,
 
-        @ApiModelProperty(example = "null", value = "pet status in the store")
-        @JsonProperty("status") var status: Pet.Status? = null
+    @ApiModelProperty(example = "null", value = "pet status in the store")
+    @JsonProperty("status") var status: Pet.Status? = null
 ) {
 
     /**
diff --git a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Tag.kt b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Tag.kt
index 3997d00edbef..ffb1ee025666 100644
--- a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Tag.kt
+++ b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/Tag.kt
@@ -16,13 +16,13 @@ import io.swagger.annotations.ApiModelProperty
  * @param id 
  * @param name 
  */
-data class Tag (
+data class Tag(
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("id") var id: kotlin.Long? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("id") var id: kotlin.Long? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("name") var name: kotlin.String? = null
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("name") var name: kotlin.String? = null
 ) {
 
 }
diff --git a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/User.kt b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/User.kt
index 011d28b1cdb8..f9e666336daf 100644
--- a/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/User.kt
+++ b/samples/server/petstore/kotlin-springboot-modelMutable/src/main/kotlin/org/openapitools/model/User.kt
@@ -22,31 +22,31 @@ import io.swagger.annotations.ApiModelProperty
  * @param phone 
  * @param userStatus User Status
  */
-data class User (
+data class User(
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("id") var id: kotlin.Long? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("id") var id: kotlin.Long? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("username") var username: kotlin.String? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("username") var username: kotlin.String? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("firstName") var firstName: kotlin.String? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("firstName") var firstName: kotlin.String? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("lastName") var lastName: kotlin.String? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("lastName") var lastName: kotlin.String? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("email") var email: kotlin.String? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("email") var email: kotlin.String? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("password") var password: kotlin.String? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("password") var password: kotlin.String? = null,
 
-        @ApiModelProperty(example = "null", value = "")
-        @JsonProperty("phone") var phone: kotlin.String? = null,
+    @ApiModelProperty(example = "null", value = "")
+    @JsonProperty("phone") var phone: kotlin.String? = null,
 
-        @ApiModelProperty(example = "null", value = "User Status")
-        @JsonProperty("userStatus") var userStatus: kotlin.Int? = null
+    @ApiModelProperty(example = "null", value = "User Status")
+    @JsonProperty("userStatus") var userStatus: kotlin.Int? = null
 ) {
 
 }
diff --git a/samples/server/petstore/kotlin/vertx/.openapi-generator/VERSION b/samples/server/petstore/kotlin/vertx/.openapi-generator/VERSION
index d168f1d8bdaa..b5d898602c2c 100644
--- a/samples/server/petstore/kotlin/vertx/.openapi-generator/VERSION
+++ b/samples/server/petstore/kotlin/vertx/.openapi-generator/VERSION
@@ -1 +1 @@
-4.2.1-SNAPSHOT
\ No newline at end of file
+4.3.1-SNAPSHOT
\ No newline at end of file
diff --git a/samples/server/petstore/kotlin/vertx/pom.xml b/samples/server/petstore/kotlin/vertx/pom.xml
index f350d61b9483..2c2af368f316 100644
--- a/samples/server/petstore/kotlin/vertx/pom.xml
+++ b/samples/server/petstore/kotlin/vertx/pom.xml
@@ -7,7 +7,7 @@
     <version>1.0.0-SNAPSHOT</version>
     <packaging>jar</packaging>
   
-    <name>OpenAPI Petstore</name>
+      <name>OpenAPI Petstore</name>
       
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
@@ -187,4 +187,4 @@
             </plugin>
         </plugins>
     </build>
-</project>
+</project>
\ No newline at end of file
diff --git a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Pet.kt b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Pet.kt
index b96a3dde895e..e80d49fc3f5f 100644
--- a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Pet.kt
+++ b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Pet.kt
@@ -20,10 +20,10 @@ import com.fasterxml.jackson.annotation.JsonIgnoreProperties
 import com.fasterxml.jackson.annotation.JsonInclude
 /**
  * A pet for sale in the pet store
- * @param id 
- * @param category 
  * @param name 
  * @param photoUrls 
+ * @param id 
+ * @param category 
  * @param tags 
  * @param status pet status in the store
  */