diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/ApiClient.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/ApiClient.mustache
index f641d8e16d96..26e1493e0373 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/ApiClient.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/ApiClient.mustache
@@ -784,6 +784,10 @@ public class ApiClient{{#jsr310}} extends JavaTimeFormatter{{/jsr310}} {
             }
         }
 
+        if (responseEntity == null) {
+            throw new RestClientException("API returned HttpServerErrorException");
+        }
+
         if (responseEntity.getStatusCode().is2xxSuccessful()) {
             return responseEntity;
         } else {
diff --git a/samples/client/echo_api/java/resttemplate/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/echo_api/java/resttemplate/src/main/java/org/openapitools/client/ApiClient.java
index cd4196b5c211..15a1b9c79b7b 100644
--- a/samples/client/echo_api/java/resttemplate/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/echo_api/java/resttemplate/src/main/java/org/openapitools/client/ApiClient.java
@@ -700,6 +700,10 @@ public <T> ResponseEntity<T> invokeAPI(String path, HttpMethod method, Map<Strin
             }
         }
 
+        if (responseEntity == null) {
+            throw new RestClientException("API returned HttpServerErrorException");
+        }
+
         if (responseEntity.getStatusCode().is2xxSuccessful()) {
             return responseEntity;
         } else {
diff --git a/samples/client/others/java/resttemplate-useAbstractionForFiles/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/others/java/resttemplate-useAbstractionForFiles/src/main/java/org/openapitools/client/ApiClient.java
index 14e600e64462..0d9f0d1498c7 100644
--- a/samples/client/others/java/resttemplate-useAbstractionForFiles/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/others/java/resttemplate-useAbstractionForFiles/src/main/java/org/openapitools/client/ApiClient.java
@@ -643,6 +643,10 @@ public <T> ResponseEntity<T> invokeAPI(String path, HttpMethod method, Map<Strin
             }
         }
 
+        if (responseEntity == null) {
+            throw new RestClientException("API returned HttpServerErrorException");
+        }
+
         if (responseEntity.getStatusCode().is2xxSuccessful()) {
             return responseEntity;
         } else {
diff --git a/samples/client/petstore/java/resttemplate-jakarta/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/resttemplate-jakarta/src/main/java/org/openapitools/client/ApiClient.java
index 6d065b370a7a..313b5ae1290f 100644
--- a/samples/client/petstore/java/resttemplate-jakarta/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/resttemplate-jakarta/src/main/java/org/openapitools/client/ApiClient.java
@@ -692,6 +692,10 @@ public <T> ResponseEntity<T> invokeAPI(String path, HttpMethod method, Map<Strin
             }
         }
 
+        if (responseEntity == null) {
+            throw new RestClientException("API returned HttpServerErrorException");
+        }
+
         if (responseEntity.getStatusCode().is2xxSuccessful()) {
             return responseEntity;
         } else {
diff --git a/samples/client/petstore/java/resttemplate-swagger1/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/resttemplate-swagger1/src/main/java/org/openapitools/client/ApiClient.java
index 446c2c721a36..da9e4a41e72c 100644
--- a/samples/client/petstore/java/resttemplate-swagger1/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/resttemplate-swagger1/src/main/java/org/openapitools/client/ApiClient.java
@@ -692,6 +692,10 @@ public <T> ResponseEntity<T> invokeAPI(String path, HttpMethod method, Map<Strin
             }
         }
 
+        if (responseEntity == null) {
+            throw new RestClientException("API returned HttpServerErrorException");
+        }
+
         if (responseEntity.getStatusCode().is2xxSuccessful()) {
             return responseEntity;
         } else {
diff --git a/samples/client/petstore/java/resttemplate-swagger2/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/resttemplate-swagger2/src/main/java/org/openapitools/client/ApiClient.java
index 446c2c721a36..da9e4a41e72c 100644
--- a/samples/client/petstore/java/resttemplate-swagger2/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/resttemplate-swagger2/src/main/java/org/openapitools/client/ApiClient.java
@@ -692,6 +692,10 @@ public <T> ResponseEntity<T> invokeAPI(String path, HttpMethod method, Map<Strin
             }
         }
 
+        if (responseEntity == null) {
+            throw new RestClientException("API returned HttpServerErrorException");
+        }
+
         if (responseEntity.getStatusCode().is2xxSuccessful()) {
             return responseEntity;
         } else {
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/ApiClient.java
index 72282e70426c..9e0aacc576a5 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/ApiClient.java
@@ -755,6 +755,10 @@ public <T> ResponseEntity<T> invokeAPI(String path, HttpMethod method, Map<Strin
             }
         }
 
+        if (responseEntity == null) {
+            throw new RestClientException("API returned HttpServerErrorException");
+        }
+
         if (responseEntity.getStatusCode().is2xxSuccessful()) {
             return responseEntity;
         } else {
diff --git a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/ApiClient.java
index f20fc5eb7cc8..1f71044281a7 100644
--- a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/ApiClient.java
@@ -750,6 +750,10 @@ public <T> ResponseEntity<T> invokeAPI(String path, HttpMethod method, Map<Strin
             }
         }
 
+        if (responseEntity == null) {
+            throw new RestClientException("API returned HttpServerErrorException");
+        }
+
         if (responseEntity.getStatusCode().is2xxSuccessful()) {
             return responseEntity;
         } else {