Prevent NPE when using pathExtension predicate

This commit ensures pathExtension predicate is skipped when the value
is null, in order to provide a more predictable behavior, and allow
a better compatibility with collections not supporting null elements
like the ones created by List#of.

Closes gh-32404

spring-webmvc/src/test/java/org/springframework/web/servlet/function/RequestPredicatesTests.java

@@ -17,6 +17,7 @@
 package org.springframework.web.servlet.function;
 
 import java.util.Collections;
+import java.util.List;
 import java.util.function.Consumer;
 import java.util.function.Function;
 
@@ -34,6 +35,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 
 /**
  * @author Arjen Poutsma
+ * @author Sebastien Deleuze
  */
 class RequestPredicatesTests {
 
@@ -232,6 +234,18 @@ class RequestPredicatesTests {
 		assertThat(predicate.test(initRequest("GET", "/FILE.TXT"))).isFalse();
 
 		assertThat(predicate.test(initRequest("GET", "/file.foo"))).isFalse();
+		assertThat(predicate.test(initRequest("GET", "/file"))).isFalse();
+	}
+
+	@Test
+	void pathExtensionPredicate() {
+		List<String> extensions = List.of("foo", "bar");
+		RequestPredicate predicate = RequestPredicates.pathExtension(extensions::contains);
+
+		assertThat(predicate.test(initRequest("GET", "/file.foo"))).isTrue();
+		assertThat(predicate.test(initRequest("GET", "/file.bar"))).isTrue();
+		assertThat(predicate.test(initRequest("GET", "/file"))).isFalse();
+		assertThat(predicate.test(initRequest("GET", "/file.baz"))).isFalse();
 	}
 
 	@Test