Refine "Redirecting to a resource" section code sample

The commit updates the code sample to use a null element friendly list.

Closes gh-32423

framework-docs/modules/ROOT/pages/web/webflux-functional.adoc

@@ -803,7 +803,7 @@ Java::
 [source,java,indent=0,subs="verbatim,quotes",role="primary"]
 ----
 	ClassPathResource index = new ClassPathResource("static/index.html");
-	List<String> extensions = List.of("js", "css", "ico", "png", "jpg", "gif");
+	List<String> extensions = Arrays.asList("js", "css", "ico", "png", "jpg", "gif");
 	RequestPredicate spaPredicate = path("/api/**").or(path("/error")).or(pathExtension(extensions::contains)).negate();
 	RouterFunction<ServerResponse> redirectToIndex = route()
 		.resource(spaPredicate, index)

framework-docs/modules/ROOT/pages/web/webmvc-functional.adoc

@@ -781,7 +781,7 @@ Java::
 [source,java,indent=0,subs="verbatim,quotes",role="primary"]
 ----
     ClassPathResource index = new ClassPathResource("static/index.html");
-	List<String> extensions = List.of("js", "css", "ico", "png", "jpg", "gif");
+	List<String> extensions = Arrays.asList("js", "css", "ico", "png", "jpg", "gif");
 	RequestPredicate spaPredicate = path("/api/**").or(path("/error")).or(pathExtension(extensions::contains)).negate();
 	RouterFunction<ServerResponse> redirectToIndex = route()
 		.resource(spaPredicate, index)