diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/vertx/ApiClient.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/vertx/ApiClient.mustache
index 90f4cbcb33b..571a3e4e63f 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/vertx/ApiClient.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/vertx/ApiClient.mustache
@@ -444,7 +444,7 @@ public class ApiClient {
 
         updateParamsForAuth(authNames, queryParams, headerParams);
 
-        if (accepts != null) {
+        if (accepts != null && accepts.length > 0) {
             headerParams.add(HttpHeaders.ACCEPT, selectHeaderAccept(accepts));
         }
 
@@ -579,7 +579,7 @@ public class ApiClient {
                             return;
                         } else {
                             try {
-                                resultContent = Json.mapper.readValue(httpResponse.bodyAsString(), returnType);
+                                resultContent = this.objectMapper.readValue(httpResponse.bodyAsString(), returnType);
                                 result = Future.succeededFuture(resultContent);
                             } catch (Exception e) {
                                 result =  ApiException.fail(new DecodeException("Failed to decode:" + e.getMessage(), e));
diff --git a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/ApiClient.java
index 4555d9a142f..84bad01a4ed 100644
--- a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/ApiClient.java
@@ -440,7 +440,7 @@ public class ApiClient {
 
         updateParamsForAuth(authNames, queryParams, headerParams);
 
-        if (accepts != null) {
+        if (accepts != null && accepts.length > 0) {
             headerParams.add(HttpHeaders.ACCEPT, selectHeaderAccept(accepts));
         }
 
@@ -575,7 +575,7 @@ public class ApiClient {
                             return;
                         } else {
                             try {
-                                resultContent = Json.mapper.readValue(httpResponse.bodyAsString(), returnType);
+                                resultContent = this.objectMapper.readValue(httpResponse.bodyAsString(), returnType);
                                 result = Future.succeededFuture(resultContent);
                             } catch (Exception e) {
                                 result =  ApiException.fail(new DecodeException("Failed to decode:" + e.getMessage(), e));