8360045: StringTokenizer.hasMoreTokens() throws NPE after nextToken(null)

Reviewed-by: liach, alanb

Author: naotoj

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1994, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1994, 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
@@ -368,6 +368,8 @@ public String nextToken() {
      * @throws    NullPointerException if delim is {@code null}
      */
     public String nextToken(String delim) {
+        Objects.requireNonNull(delim);
+
         delimiters = delim;
 
         /* delimiter string specified, so set the appropriate flag. */

test/jdk/java/util/StringTokenizer/NextTokenWithNullDelimTest.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8360045
+ * @summary Verify StringTokenizer.nextToken(null) does not alter the
+ *      existing delimiter
+ * @run junit NextTokenWithNullDelimTest
+ */
+
+import java.util.StringTokenizer;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class NextTokenWithNullDelimTest {
+    @Test
+    void testNextTokenWithNullDelim() {
+        StringTokenizer st = new StringTokenizer("test");
+        assertThrows(NullPointerException.class, () -> st.nextToken(null));
+        assertDoesNotThrow(st::hasMoreTokens);
+    }
+}