8369452: Locale.Builder.setLanguageTag(String) does not clear on empty or null String

Reviewed-by: naoto

Author: Justin Lu

src/java.base/share/classes/java/util/Locale.java

@@ -2726,9 +2726,13 @@ public Builder setLocale(Locale locale) {
          * @see Locale#forLanguageTag(String)
          */
         public Builder setLanguageTag(String languageTag) {
-            LanguageTag tag = LanguageTag.parse(
-                    languageTag, new ParsePosition(0), false);
-            localeBuilder.setLanguageTag(tag);
+            if (LocaleUtils.isEmpty(languageTag)) {
+                localeBuilder.clear();
+            } else {
+                LanguageTag tag = LanguageTag.parse(
+                        languageTag, new ParsePosition(0), false);
+                localeBuilder.setLanguageTag(tag);
+            }
             return this;
         }
 

test/jdk/java/util/Locale/LocaleEnhanceTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2010, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -42,13 +42,17 @@
 import java.util.Set;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.EmptySource;
+import org.junit.jupiter.params.provider.NullSource;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.fail;
 
 /**
  * @test
  * @bug 6875847 6992272 7002320 7015500 7023613 7032820 7033504 7004603
- *    7044019 8008577 8176853 8255086 8263202 8287868 8174269
+ *      7044019 8008577 8176853 8255086 8263202 8287868 8174269 8369452
  * @summary test API changes to Locale
  * @modules jdk.localedata
  * @compile LocaleEnhanceTest.java
@@ -763,6 +767,20 @@ public void testBuilderSetLanguageTag() {
         new BuilderILE() { public void call() { b.setLanguageTag("und-u-nu-thai-NU-chinese-xx-1234"); }};
     }
 
+    // Test the values that should clear the builder
+    @ParameterizedTest
+    @NullSource
+    @EmptySource
+    public void testBuilderSetLanguageTagClear(String tag) {
+        var empty = new Builder();
+        var bldr = new Builder();
+        bldr.setLanguageTag("en-US");
+        assertDoesNotThrow(() -> bldr.setLanguageTag(tag));
+        assertEquals("Setting a %s language tag did not clear the builder"
+                .formatted(tag == null ? "null" : "empty"),
+                empty.build(), bldr.build());
+    }
+
     @Test
     public void testBuilderSetLanguage() {
         // language is normalized to lower case