diff --git a/pom.xml b/pom.xml
index f5087028da65..4f7cb54b224a 100644
--- a/pom.xml
+++ b/pom.xml
@@ -1243,9 +1243,9 @@
                 <module>samples/client/petstore/elixir</module>
                 <module>samples/client/petstore/erlang-client</module>
                 <module>samples/client/petstore/erlang-proper</module>
-                <!--<module>samples/client/petstore/kotlin/</module>
+                <module>samples/client/petstore/kotlin/</module>
                 <module>samples/client/petstore/kotlin-threetenbp/</module>
-                <module>samples/client/petstore/kotlin-string/</module>-->
+                <module>samples/client/petstore/kotlin-string/</module>
                 <!-- servers -->
                 <module>samples/server/petstore/erlang-server</module>
                 <module>samples/server/petstore/jaxrs/jersey2</module>
diff --git a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
index e6ebe7982db1..def00253aed0 100644
--- a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
+++ b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
@@ -74,10 +74,12 @@ open class ApiClient(val baseUrl: String) {
 
     protected fun updateAuthParams(requestConfig: RequestConfig) {
         if (requestConfig.headers["api_key"].isNullOrEmpty()) {
-            if (apiKeyPrefix["api_key"] != null) {
-                requestConfig.headers["api_key"] = apiKeyPrefix["api_key"] + " " + apiKey["api_key"]
-            } else {
-                requestConfig.headers["api_key"] = apiKey["api_key"]
+            if (apiKey["api_key"] != null) {
+                if (apiKeyPrefix["api_key"] != null) {
+                    requestConfig.headers["api_key"] = apiKeyPrefix["api_key"]!! + " " + apiKey["api_key"]!!
+                } else {
+                    requestConfig.headers["api_key"] = apiKey["api_key"]!!
+                }
             }
         }
         if (requestConfig.headers[Authorization].isNullOrEmpty()) {
diff --git a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
index e6ebe7982db1..def00253aed0 100644
--- a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
+++ b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt
@@ -74,10 +74,12 @@ open class ApiClient(val baseUrl: String) {
 
     protected fun updateAuthParams(requestConfig: RequestConfig) {
         if (requestConfig.headers["api_key"].isNullOrEmpty()) {
-            if (apiKeyPrefix["api_key"] != null) {
-                requestConfig.headers["api_key"] = apiKeyPrefix["api_key"] + " " + apiKey["api_key"]
-            } else {
-                requestConfig.headers["api_key"] = apiKey["api_key"]
+            if (apiKey["api_key"] != null) {
+                if (apiKeyPrefix["api_key"] != null) {
+                    requestConfig.headers["api_key"] = apiKeyPrefix["api_key"]!! + " " + apiKey["api_key"]!!
+                } else {
+                    requestConfig.headers["api_key"] = apiKey["api_key"]!!
+                }
             }
         }
         if (requestConfig.headers[Authorization].isNullOrEmpty()) {