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 87f6c5f1016..41db79fc8e5 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
@@ -251,7 +251,9 @@ public class ApiClient {
   }
 
   private void updateBasePath() {
-    setBasePath(servers.get(serverIndex).URL(serverVariables));
+    if (serverIndex != null) {
+        setBasePath(servers.get(serverIndex).URL(serverVariables));
+    }
   }
 
   {{#hasOAuthMethods}}
@@ -1030,7 +1032,7 @@ public class ApiClient {
     // Not using `.target(targetURL).path(path)` below,
     // to support (constant) query string in `path`, e.g. "/posts?draft=1"
     String targetURL;
-    if (operationServers.containsKey(operation)) {
+    if (serverIndex != null && operationServers.containsKey(operation)) {
       Integer index = operationServerIndex.containsKey(operation) ? operationServerIndex.get(operation) : serverIndex;
       Map<String, String> variables = operationServerVariables.containsKey(operation) ?
         operationServerVariables.get(operation) : serverVariables;
diff --git a/samples/client/petstore/java/jersey2-java7/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/jersey2-java7/src/main/java/org/openapitools/client/ApiClient.java
index 2da5dacd44d..36afb9066fb 100644
--- a/samples/client/petstore/java/jersey2-java7/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/jersey2-java7/src/main/java/org/openapitools/client/ApiClient.java
@@ -168,7 +168,9 @@ public class ApiClient {
   }
 
   private void updateBasePath() {
-    setBasePath(servers.get(serverIndex).URL(serverVariables));
+    if (serverIndex != null) {
+        setBasePath(servers.get(serverIndex).URL(serverVariables));
+    }
   }
 
   private void setOauthBasePath(String basePath) {
@@ -937,7 +939,7 @@ public class ApiClient {
     // Not using `.target(targetURL).path(path)` below,
     // to support (constant) query string in `path`, e.g. "/posts?draft=1"
     String targetURL;
-    if (operationServers.containsKey(operation)) {
+    if (serverIndex != null && operationServers.containsKey(operation)) {
       Integer index = operationServerIndex.containsKey(operation) ? operationServerIndex.get(operation) : serverIndex;
       Map<String, String> variables = operationServerVariables.containsKey(operation) ?
         operationServerVariables.get(operation) : serverVariables;
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 2da5dacd44d..36afb9066fb 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
@@ -168,7 +168,9 @@ public class ApiClient {
   }
 
   private void updateBasePath() {
-    setBasePath(servers.get(serverIndex).URL(serverVariables));
+    if (serverIndex != null) {
+        setBasePath(servers.get(serverIndex).URL(serverVariables));
+    }
   }
 
   private void setOauthBasePath(String basePath) {
@@ -937,7 +939,7 @@ public class ApiClient {
     // Not using `.target(targetURL).path(path)` below,
     // to support (constant) query string in `path`, e.g. "/posts?draft=1"
     String targetURL;
-    if (operationServers.containsKey(operation)) {
+    if (serverIndex != null && operationServers.containsKey(operation)) {
       Integer index = operationServerIndex.containsKey(operation) ? operationServerIndex.get(operation) : serverIndex;
       Map<String, String> variables = operationServerVariables.containsKey(operation) ?
         operationServerVariables.get(operation) : serverVariables;