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 90a3758eba2..72949027876 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
@@ -1,6 +1,7 @@
 package org.openapitools.client;
 
 import org.openapitools.client.auth.*;
+import org.openapitools.client.RFC3339DateFormat;
 
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
@@ -18,6 +19,13 @@ public class ApiClientTest {
         apiClient = new ApiClient();
     }
 
+    @Test
+    public void testRFC3339DateFormat() {
+        // test the constructor and the clone method to ensure there's no NPE
+        RFC3339DateFormat r = new RFC3339DateFormat();
+        RFC3339DateFormat r2 = (RFC3339DateFormat) r.clone();
+    }
+
     @Test
     public void testParseAndFormatDate() {
         // default date format