diff --git a/deepl-java/src/main/java/com/deepl/api/DeepLApiVersion.java b/deepl-java/src/main/java/com/deepl/api/DeepLApiVersion.java
index 5725fbb..19a5768 100644
--- a/deepl-java/src/main/java/com/deepl/api/DeepLApiVersion.java
+++ b/deepl-java/src/main/java/com/deepl/api/DeepLApiVersion.java
@@ -1,3 +1,6 @@
+// Copyright 2025 DeepL SE (https://www.deepl.com)
+// Use of this source code is governed by an MIT
+// license that can be found in the LICENSE file.
 package com.deepl.api;
 
 public enum DeepLApiVersion {
diff --git a/deepl-java/src/main/java/com/deepl/api/Translator.java b/deepl-java/src/main/java/com/deepl/api/Translator.java
index b259c55..97f6a1c 100644
--- a/deepl-java/src/main/java/com/deepl/api/Translator.java
+++ b/deepl-java/src/main/java/com/deepl/api/Translator.java
@@ -42,20 +42,24 @@ public class Translator {
    */
   @Deprecated
   public Translator(String authKey, TranslatorOptions options) throws IllegalArgumentException {
-    if (authKey == null || authKey.length() == 0) {
-      throw new IllegalArgumentException("authKey must be a non-empty string");
+    if (authKey == null || authKey.isEmpty()) {
+      throw new IllegalArgumentException("authKey cannot be null or empty");
     }
+
+    String sanitizedAuthKey = authKey.trim();
     this.apiVersion = options.apiVersion;
     String serverUrl =
         (options.getServerUrl() != null)
             ? options.getServerUrl()
-            : (isFreeAccountAuthKey(authKey) ? DEEPL_SERVER_URL_FREE : DEEPL_SERVER_URL_PRO);
+            : (isFreeAccountAuthKey(sanitizedAuthKey)
+                ? DEEPL_SERVER_URL_FREE
+                : DEEPL_SERVER_URL_PRO);
 
     Map<String, String> headers = new HashMap<>();
     if (options.getHeaders() != null) {
       headers.putAll(options.getHeaders());
     }
-    headers.putIfAbsent("Authorization", "DeepL-Auth-Key " + authKey);
+    headers.putIfAbsent("Authorization", "DeepL-Auth-Key " + sanitizedAuthKey);
     headers.putIfAbsent(
         "User-Agent",
         constructUserAgentString(options.getSendPlatformInfo(), options.getAppInfo()));
diff --git a/deepl-java/src/test/java/com/deepl/api/GeneralTest.java b/deepl-java/src/test/java/com/deepl/api/GeneralTest.java
index b10df25..9d22ed1 100644
--- a/deepl-java/src/test/java/com/deepl/api/GeneralTest.java
+++ b/deepl-java/src/test/java/com/deepl/api/GeneralTest.java
@@ -29,6 +29,16 @@ void testEmptyAuthKey() {
             });
   }
 
+  @Test
+  void testNullAuthKey() {
+    IllegalArgumentException thrown =
+        Assertions.assertThrows(
+            IllegalArgumentException.class,
+            () -> {
+              Translator translator = new Translator(null);
+            });
+  }
+
   @Test
   void testInvalidAuthKey() {
     String authKey = "invalid";