diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/api.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/api.mustache
index c86a00b405d..12726a03057 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/api.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/api.mustache
@@ -41,7 +41,6 @@ class {{classname}}(basePath: kotlin.String = "{{{basePath}}}") : ApiClient(base
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
diff --git a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/PetApi.kt b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
index 83e8ec2abf0..c153034537d 100644
--- a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
+++ b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
@@ -45,7 +45,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -77,7 +76,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -109,7 +107,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -141,7 +138,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -173,7 +169,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -204,7 +199,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -237,7 +231,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -271,7 +264,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
diff --git a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
index bead1dcc359..f54c7c9fb64 100644
--- a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
+++ b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
@@ -44,7 +44,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -75,7 +74,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -107,7 +105,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -139,7 +136,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
diff --git a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/UserApi.kt b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
index 130def3847f..408c47da34e 100644
--- a/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
+++ b/samples/client/petstore/kotlin-string/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
@@ -44,7 +44,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -75,7 +74,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -106,7 +104,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -137,7 +134,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -169,7 +165,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -202,7 +197,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -232,7 +226,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -264,7 +257,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
diff --git a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/PetApi.kt b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
index 9c6df9475da..7b872396d52 100644
--- a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
+++ b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
@@ -46,7 +46,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -78,7 +77,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -110,7 +108,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -142,7 +139,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -174,7 +170,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -205,7 +200,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -238,7 +232,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -272,7 +265,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
diff --git a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
index 518113b4708..c281c967267 100644
--- a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
+++ b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
@@ -45,7 +45,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -76,7 +75,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -108,7 +106,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -140,7 +137,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
diff --git a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/UserApi.kt b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
index 2e7ed153438..301d20d91ce 100644
--- a/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
+++ b/samples/client/petstore/kotlin-threetenbp/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
@@ -45,7 +45,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -76,7 +75,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -107,7 +105,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -138,7 +135,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -170,7 +166,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -203,7 +198,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -233,7 +227,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -265,7 +258,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
diff --git a/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/PetApi.kt b/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
index 83e8ec2abf0..c153034537d 100644
--- a/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
+++ b/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
@@ -45,7 +45,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -77,7 +76,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -109,7 +107,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -141,7 +138,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -173,7 +169,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -204,7 +199,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -237,7 +231,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -271,7 +264,6 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
diff --git a/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt b/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
index bead1dcc359..f54c7c9fb64 100644
--- a/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
+++ b/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
@@ -44,7 +44,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -75,7 +74,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -107,7 +105,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -139,7 +136,6 @@ class StoreApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiC
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
diff --git a/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/UserApi.kt b/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
index 130def3847f..408c47da34e 100644
--- a/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
+++ b/samples/client/petstore/kotlin/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
@@ -44,7 +44,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -75,7 +74,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -106,7 +104,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -137,7 +134,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -169,7 +165,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -202,7 +197,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -232,7 +226,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }
 
@@ -264,7 +257,6 @@ class UserApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCl
             ResponseType.Redirection -> TODO()
             ResponseType.ClientError -> throw ClientException((response as ClientError<*>).body as? String ?: "Client error")
             ResponseType.ServerError -> throw ServerException((response as ServerError<*>).message ?: "Server error")
-            else -> throw kotlin.IllegalStateException("Undefined ResponseType.")
         }
     }