src/java.base/share/classes/java/net/CookieManager.java

@@ -199,14 +199,13 @@
         // pre-condition check
         if (uri == null || requestHeaders == null) {
             throw new IllegalArgumentException("Argument is null");
         }
 
-        Map<String, List<String>> cookieMap = new java.util.HashMap<>();
         // if there's no default CookieStore, no way for us to get any cookie
         if (cookieJar == null)
-            return Collections.unmodifiableMap(cookieMap);
+            return Map.of();
 
         boolean secureLink = "https".equalsIgnoreCase(uri.getScheme());
         List<HttpCookie> cookies = new java.util.ArrayList<>();
         String path = uri.getPath();
         if (path == null || path.isEmpty()) {

@@ -242,12 +241,11 @@
         }
 
         // apply sort rule (RFC 2965 sec. 3.3.4)
         List<String> cookieHeader = sortByPath(cookies);
 
-        cookieMap.put("Cookie", cookieHeader);
-        return Collections.unmodifiableMap(cookieMap);
+        return Map.of("Cookie", cookieHeader);
     }
 
     public void
         put(URI uri, Map<String, List<String>> responseHeaders)
         throws IOException