diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/jersey2/ApiClient.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/jersey2/ApiClient.mustache
index 286838dcff45..cef315b6c5e9 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/jersey2/ApiClient.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/jersey2/ApiClient.mustache
@@ -915,17 +915,23 @@ public class ApiClient{{#jsr310}} extends JavaTimeFormatter{{/jsr310}} {
    *
    * @param contentTypes The Content-Type array to select from
    * @return The Content-Type header to use. If the given array is empty,
-   *   JSON will be used.
+   *   returns null. If it matches "any", JSON will be used.
    */
   public String selectHeaderContentType(String[] contentTypes) {
     if (contentTypes.length == 0) {
+      return null;
+    }
+
+    if (contentTypes[0].equals("*/*")) {
       return "application/json";
     }
+
     for (String contentType : contentTypes) {
       if (isJsonMime(contentType)) {
         return contentType;
       }
     }
+
     return contentTypes[0];
   }
 
@@ -955,7 +961,9 @@ public class ApiClient{{#jsr310}} extends JavaTimeFormatter{{/jsr310}} {
    */
   public Entity<?> serialize(Object obj, Map<String, Object> formParams, String contentType, boolean isBodyNullable) throws ApiException {
     Entity<?> entity;
-    if (contentType.startsWith("multipart/form-data")) {
+    if (contentType == null) {
+      return null;
+    } else if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
         if (param.getValue() instanceof File) {
@@ -1000,12 +1008,15 @@ public class ApiClient{{#jsr310}} extends JavaTimeFormatter{{/jsr310}} {
    *
    * @param obj Object
    * @param formParams Form parameters
-   * @param contentType Context type
+   * @param contentType Content type
    * @param isBodyNullable True if the body is nullable
    * @return String
    * @throws ApiException API exception
    */
   public String serializeToString(Object obj, Map<String, Object> formParams, String contentType, boolean isBodyNullable) throws ApiException {
+    if (contentType == null) {
+      return null;
+    }
     try {
       if (contentType.startsWith("multipart/form-data")) {
         throw new ApiException("multipart/form-data not yet supported for serializeToString (http signature authentication)");
diff --git a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/ApiClient.java
index 5f4cb48efe22..2867c1c5ac69 100644
--- a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/ApiClient.java
@@ -831,17 +831,23 @@ public String selectHeaderAccept(String[] accepts) {
    *
    * @param contentTypes The Content-Type array to select from
    * @return The Content-Type header to use. If the given array is empty,
-   *   JSON will be used.
+   *   returns null. If it matches "any", JSON will be used.
    */
   public String selectHeaderContentType(String[] contentTypes) {
     if (contentTypes.length == 0) {
+      return null;
+    }
+
+    if (contentTypes[0].equals("*/*")) {
       return "application/json";
     }
+
     for (String contentType : contentTypes) {
       if (isJsonMime(contentType)) {
         return contentType;
       }
     }
+
     return contentTypes[0];
   }
 
@@ -871,7 +877,9 @@ public String escapeString(String str) {
    */
   public Entity<?> serialize(Object obj, Map<String, Object> formParams, String contentType, boolean isBodyNullable) throws ApiException {
     Entity<?> entity;
-    if (contentType.startsWith("multipart/form-data")) {
+    if (contentType == null) {
+      return null;
+    } else if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
         if (param.getValue() instanceof File) {
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java
index 5f4cb48efe22..2c0d233e303c 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java
@@ -831,17 +831,23 @@ public String selectHeaderAccept(String[] accepts) {
    *
    * @param contentTypes The Content-Type array to select from
    * @return The Content-Type header to use. If the given array is empty,
-   *   JSON will be used.
+   *   returns null. If it matches "any", JSON will be used.
    */
   public String selectHeaderContentType(String[] contentTypes) {
     if (contentTypes.length == 0) {
+      return null;
+    }
+
+    if (contentTypes[0].equals("*/*")) {
       return "application/json";
     }
+
     for (String contentType : contentTypes) {
       if (isJsonMime(contentType)) {
         return contentType;
       }
     }
+
     return contentTypes[0];
   }
 
@@ -871,7 +877,9 @@ public String escapeString(String str) {
    */
   public Entity<?> serialize(Object obj, Map<String, Object> formParams, String contentType, boolean isBodyNullable) throws ApiException {
     Entity<?> entity;
-    if (contentType.startsWith("multipart/form-data")) {
+    if (contentType == null) {
+      return null;
+    } else if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
         if (param.getValue() instanceof File) {
@@ -916,12 +924,15 @@ public Entity<?> serialize(Object obj, Map<String, Object> formParams, String co
    *
    * @param obj Object
    * @param formParams Form parameters
-   * @param contentType Context type
+   * @param contentType Content type
    * @param isBodyNullable True if the body is nullable
    * @return String
    * @throws ApiException API exception
    */
   public String serializeToString(Object obj, Map<String, Object> formParams, String contentType, boolean isBodyNullable) throws ApiException {
+    if (contentType == null) {
+      return null;
+    }
     try {
       if (contentType.startsWith("multipart/form-data")) {
         throw new ApiException("multipart/form-data not yet supported for serializeToString (http signature authentication)");
diff --git a/samples/client/petstore/java/jersey2-java8/src/test/java/org/openapitools/client/ApiClientTest.java b/samples/client/petstore/java/jersey2-java8/src/test/java/org/openapitools/client/ApiClientTest.java
index 90a3758eba24..20d01ee9be3b 100644
--- a/samples/client/petstore/java/jersey2-java8/src/test/java/org/openapitools/client/ApiClientTest.java
+++ b/samples/client/petstore/java/jersey2-java8/src/test/java/org/openapitools/client/ApiClientTest.java
@@ -95,7 +95,7 @@ public void testSelectHeaderContentType() {
         assertEquals("text/plain", apiClient.selectHeaderContentType(contentTypes));
 
         contentTypes = new String[]{};
-        assertEquals("application/json", apiClient.selectHeaderContentType(contentTypes));
+        assertNull(apiClient.selectHeaderContentType(contentTypes));
     }
 
     @Test
diff --git a/samples/openapi3/client/extensions/x-auth-id-alias/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java b/samples/openapi3/client/extensions/x-auth-id-alias/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java
index 7f844074052a..e1ac74328ea0 100644
--- a/samples/openapi3/client/extensions/x-auth-id-alias/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/openapi3/client/extensions/x-auth-id-alias/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java
@@ -761,17 +761,23 @@ public String selectHeaderAccept(String[] accepts) {
    *
    * @param contentTypes The Content-Type array to select from
    * @return The Content-Type header to use. If the given array is empty,
-   *   JSON will be used.
+   *   returns null. If it matches "any", JSON will be used.
    */
   public String selectHeaderContentType(String[] contentTypes) {
     if (contentTypes.length == 0) {
+      return null;
+    }
+
+    if (contentTypes[0].equals("*/*")) {
       return "application/json";
     }
+
     for (String contentType : contentTypes) {
       if (isJsonMime(contentType)) {
         return contentType;
       }
     }
+
     return contentTypes[0];
   }
 
@@ -801,7 +807,9 @@ public String escapeString(String str) {
    */
   public Entity<?> serialize(Object obj, Map<String, Object> formParams, String contentType, boolean isBodyNullable) throws ApiException {
     Entity<?> entity;
-    if (contentType.startsWith("multipart/form-data")) {
+    if (contentType == null) {
+      return null;
+    } else if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
         if (param.getValue() instanceof File) {
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8-special-characters/src/main/java/org/openapitools/client/ApiClient.java b/samples/openapi3/client/petstore/java/jersey2-java8-special-characters/src/main/java/org/openapitools/client/ApiClient.java
index 66eb9ca7f90a..936bed24e080 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8-special-characters/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8-special-characters/src/main/java/org/openapitools/client/ApiClient.java
@@ -706,17 +706,23 @@ public String selectHeaderAccept(String[] accepts) {
    *
    * @param contentTypes The Content-Type array to select from
    * @return The Content-Type header to use. If the given array is empty,
-   *   JSON will be used.
+   *   returns null. If it matches "any", JSON will be used.
    */
   public String selectHeaderContentType(String[] contentTypes) {
     if (contentTypes.length == 0) {
+      return null;
+    }
+
+    if (contentTypes[0].equals("*/*")) {
       return "application/json";
     }
+
     for (String contentType : contentTypes) {
       if (isJsonMime(contentType)) {
         return contentType;
       }
     }
+
     return contentTypes[0];
   }
 
@@ -746,7 +752,9 @@ public String escapeString(String str) {
    */
   public Entity<?> serialize(Object obj, Map<String, Object> formParams, String contentType, boolean isBodyNullable) throws ApiException {
     Entity<?> entity;
-    if (contentType.startsWith("multipart/form-data")) {
+    if (contentType == null) {
+      return null;
+    } else if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
         if (param.getValue() instanceof File) {
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java
index 328fec6af920..1e6fbf590636 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java
@@ -915,17 +915,23 @@ public String selectHeaderAccept(String[] accepts) {
    *
    * @param contentTypes The Content-Type array to select from
    * @return The Content-Type header to use. If the given array is empty,
-   *   JSON will be used.
+   *   returns null. If it matches "any", JSON will be used.
    */
   public String selectHeaderContentType(String[] contentTypes) {
     if (contentTypes.length == 0) {
+      return null;
+    }
+
+    if (contentTypes[0].equals("*/*")) {
       return "application/json";
     }
+
     for (String contentType : contentTypes) {
       if (isJsonMime(contentType)) {
         return contentType;
       }
     }
+
     return contentTypes[0];
   }
 
@@ -955,7 +961,9 @@ public String escapeString(String str) {
    */
   public Entity<?> serialize(Object obj, Map<String, Object> formParams, String contentType, boolean isBodyNullable) throws ApiException {
     Entity<?> entity;
-    if (contentType.startsWith("multipart/form-data")) {
+    if (contentType == null) {
+      return null;
+    } else if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
         if (param.getValue() instanceof File) {