diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson-nextgen/api.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson-nextgen/api.mustache
index e0d605818d3..943e6948de7 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson-nextgen/api.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson-nextgen/api.mustache
@@ -173,7 +173,7 @@ public class {{classname}} {
             {{#consumes}}"{{{mediaType}}}"{{^-last}}, {{/-last}}{{/consumes}}
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/api.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/api.mustache
index c55259c44fe..e81f874f1e1 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/api.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/api.mustache
@@ -204,7 +204,7 @@ public class {{classname}} {
             {{#consumes}}"{{{mediaType}}}"{{^-last}}, {{/-last}}{{/consumes}}
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/others/java/okhttp-gson-streaming/src/main/java/org/openapitools/client/api/PingApi.java b/samples/client/others/java/okhttp-gson-streaming/src/main/java/org/openapitools/client/api/PingApi.java
index 5f408920f53..dc64eace544 100644
--- a/samples/client/others/java/okhttp-gson-streaming/src/main/java/org/openapitools/client/api/PingApi.java
+++ b/samples/client/others/java/okhttp-gson-streaming/src/main/java/org/openapitools/client/api/PingApi.java
@@ -123,7 +123,7 @@ public class PingApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/AnotherFakeApi.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
index 815719efc1f..5f6571f9e7d 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
@@ -133,7 +133,7 @@ public class AnotherFakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/FakeApi.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/FakeApi.java
index c7332815b44..c55d1e12c08 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/FakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/FakeApi.java
@@ -141,7 +141,7 @@ public class FakeApi {
             "application/xml", "application/xml; charset=utf-8", "application/xml; charset=utf-16", "text/xml", "text/xml; charset=utf-8", "text/xml; charset=utf-16"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -272,7 +272,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -402,7 +402,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -532,7 +532,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -662,7 +662,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -792,7 +792,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -925,7 +925,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1064,7 +1064,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1269,7 +1269,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1479,7 +1479,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1623,7 +1623,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1844,7 +1844,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1984,7 +1984,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -2132,7 +2132,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
index 2483077a5c8..c508d0d8bb6 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
@@ -133,7 +133,7 @@ public class FakeClassnameTags123Api {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/PetApi.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/PetApi.java
index e5ba0411588..085d9f0ec8e 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/PetApi.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/PetApi.java
@@ -137,7 +137,7 @@ public class PetApi {
             "application/json", "application/xml"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -275,7 +275,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -414,7 +414,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -556,7 +556,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -704,7 +704,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -848,7 +848,7 @@ public class PetApi {
             "application/json", "application/xml"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -999,7 +999,7 @@ public class PetApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1147,7 +1147,7 @@ public class PetApi {
             "multipart/form-data"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1299,7 +1299,7 @@ public class PetApi {
             "multipart/form-data"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/StoreApi.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/StoreApi.java
index 1e32b8c7607..afa9b5c026d 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/StoreApi.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/StoreApi.java
@@ -135,7 +135,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -268,7 +268,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -398,7 +398,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -540,7 +540,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/UserApi.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/UserApi.java
index faf4e626946..2051423374c 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/UserApi.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/api/UserApi.java
@@ -134,7 +134,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -265,7 +265,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -396,7 +396,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -529,7 +529,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -666,7 +666,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -811,7 +811,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -956,7 +956,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1082,7 +1082,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/AnotherFakeApi.java b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
index 9482a5a5f86..52c19920a97 100644
--- a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
@@ -91,7 +91,7 @@ public class AnotherFakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/DefaultApi.java b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/DefaultApi.java
index 70e9788eb14..7741b8200a9 100644
--- a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/DefaultApi.java
+++ b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/DefaultApi.java
@@ -90,7 +90,7 @@ public class DefaultApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/FakeApi.java b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/FakeApi.java
index 0e4cf97f1c8..d413cd3e829 100644
--- a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/FakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/FakeApi.java
@@ -98,7 +98,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -209,7 +209,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -323,7 +323,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -437,7 +437,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -551,7 +551,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -664,7 +664,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -780,7 +780,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -897,7 +897,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1086,7 +1086,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1292,7 +1292,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1432,7 +1432,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1631,7 +1631,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1749,7 +1749,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1890,7 +1890,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
index 1fac7240705..34c9d282281 100644
--- a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
+++ b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
@@ -91,7 +91,7 @@ public class FakeClassnameTags123Api {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/PetApi.java b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/PetApi.java
index c1523ef0790..8c8a226d0cb 100644
--- a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/PetApi.java
+++ b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/PetApi.java
@@ -93,7 +93,7 @@ public class PetApi {
             "application/json", "application/xml"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -208,7 +208,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -325,7 +325,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -454,7 +454,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -586,7 +586,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -713,7 +713,7 @@ public class PetApi {
             "application/json", "application/xml"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -839,7 +839,7 @@ public class PetApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -965,7 +965,7 @@ public class PetApi {
             "multipart/form-data"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1101,7 +1101,7 @@ public class PetApi {
             "multipart/form-data"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/StoreApi.java b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/StoreApi.java
index 5d93e632223..f57a9e3ff70 100644
--- a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/StoreApi.java
+++ b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/StoreApi.java
@@ -93,7 +93,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -204,7 +204,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -318,7 +318,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -444,7 +444,7 @@ public class StoreApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/UserApi.java b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/UserApi.java
index 56c6433a490..f6d5e33327c 100644
--- a/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/UserApi.java
+++ b/samples/client/petstore/java/okhttp-gson-nextgen/src/main/java/org/openapitools/client/api/UserApi.java
@@ -92,7 +92,7 @@ public class UserApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -201,7 +201,7 @@ public class UserApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -310,7 +310,7 @@ public class UserApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -421,7 +421,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -536,7 +536,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -671,7 +671,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -800,7 +800,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -904,7 +904,7 @@ public class UserApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/AnotherFakeApi.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
index af9e915240d..5789ec8083b 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
@@ -122,7 +122,7 @@ public class AnotherFakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/FakeApi.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/FakeApi.java
index b27961d1479..450dbb1a5b7 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/FakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/FakeApi.java
@@ -130,7 +130,7 @@ public class FakeApi {
             "application/xml", "application/xml; charset=utf-8", "application/xml; charset=utf-16", "text/xml", "text/xml; charset=utf-8", "text/xml; charset=utf-16"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -253,7 +253,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -375,7 +375,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -497,7 +497,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -619,7 +619,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -741,7 +741,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -869,7 +869,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1000,7 +1000,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1197,7 +1197,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1417,7 +1417,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1571,7 +1571,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1784,7 +1784,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1916,7 +1916,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -2071,7 +2071,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
index d6bac0d84af..e9e0d6cb8c9 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
@@ -122,7 +122,7 @@ public class FakeClassnameTags123Api {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/PetApi.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/PetApi.java
index 2f90b4257f9..580a5f993ce 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/PetApi.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/PetApi.java
@@ -126,7 +126,7 @@ public class PetApi {
             "application/json", "application/xml"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -259,7 +259,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -393,7 +393,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -530,7 +530,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -670,7 +670,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -806,7 +806,7 @@ public class PetApi {
             "application/json", "application/xml"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -949,7 +949,7 @@ public class PetApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1089,7 +1089,7 @@ public class PetApi {
             "multipart/form-data"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1233,7 +1233,7 @@ public class PetApi {
             "multipart/form-data"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/StoreApi.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/StoreApi.java
index 9aeea0062d0..e17f7df6c48 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/StoreApi.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/StoreApi.java
@@ -124,7 +124,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -249,7 +249,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -371,7 +371,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -505,7 +505,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/UserApi.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/UserApi.java
index abf14e6dba3..627f7880487 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/UserApi.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/api/UserApi.java
@@ -123,7 +123,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -246,7 +246,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -369,7 +369,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -494,7 +494,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -623,7 +623,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -766,7 +766,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -903,7 +903,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1021,7 +1021,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
index af9e915240d..5789ec8083b 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
@@ -122,7 +122,7 @@ public class AnotherFakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/FakeApi.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/FakeApi.java
index b27961d1479..450dbb1a5b7 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/FakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/FakeApi.java
@@ -130,7 +130,7 @@ public class FakeApi {
             "application/xml", "application/xml; charset=utf-8", "application/xml; charset=utf-16", "text/xml", "text/xml; charset=utf-8", "text/xml; charset=utf-16"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -253,7 +253,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -375,7 +375,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -497,7 +497,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -619,7 +619,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -741,7 +741,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -869,7 +869,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1000,7 +1000,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1197,7 +1197,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1417,7 +1417,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1571,7 +1571,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1784,7 +1784,7 @@ public class FakeApi {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1916,7 +1916,7 @@ public class FakeApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -2071,7 +2071,7 @@ public class FakeApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
index d6bac0d84af..e9e0d6cb8c9 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
@@ -122,7 +122,7 @@ public class FakeClassnameTags123Api {
             "application/json"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/PetApi.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/PetApi.java
index 2f90b4257f9..580a5f993ce 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/PetApi.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/PetApi.java
@@ -126,7 +126,7 @@ public class PetApi {
             "application/json", "application/xml"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -259,7 +259,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -393,7 +393,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -530,7 +530,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -670,7 +670,7 @@ public class PetApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -806,7 +806,7 @@ public class PetApi {
             "application/json", "application/xml"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -949,7 +949,7 @@ public class PetApi {
             "application/x-www-form-urlencoded"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1089,7 +1089,7 @@ public class PetApi {
             "multipart/form-data"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1233,7 +1233,7 @@ public class PetApi {
             "multipart/form-data"
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/StoreApi.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/StoreApi.java
index 9aeea0062d0..e17f7df6c48 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/StoreApi.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/StoreApi.java
@@ -124,7 +124,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -249,7 +249,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -371,7 +371,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -505,7 +505,7 @@ public class StoreApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/UserApi.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/UserApi.java
index abf14e6dba3..627f7880487 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/UserApi.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/UserApi.java
@@ -123,7 +123,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -246,7 +246,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -369,7 +369,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -494,7 +494,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -623,7 +623,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -766,7 +766,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -903,7 +903,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }
 
@@ -1021,7 +1021,7 @@ public class UserApi {
             
         };
         final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
-        if (localVarHeaderParams != null && localVarContentTypes != null) {
+        if (localVarContentType != null) {
             localVarHeaderParams.put("Content-Type", localVarContentType);
         }