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-webflux/src/main/java/org/springframework/web/reactive/function/server/RequestPredicates.java

@@ -843,7 +843,7 @@ public PathExtensionPredicate(String extension) {
 		@Override
 		public boolean test(ServerRequest request) {
 			String pathExtension = UriUtils.extractFileExtension(request.path());
-			return this.extensionPredicate.test(pathExtension);
+			return (pathExtension != null && this.extensionPredicate.test(pathExtension));
 		}
 
 		@Override

spring-webflux/src/test/java/org/springframework/web/reactive/function/server/RequestPredicatesTests.java

@@ -18,6 +18,7 @@
 
 import java.net.URI;
 import java.util.Collections;
+import java.util.List;
 import java.util.function.Function;
 
 import org.junit.jupiter.api.Test;
@@ -33,6 +34,7 @@
 
 /**
  * @author Arjen Poutsma
+ * @author Sebastien Deleuze
  */
 class RequestPredicatesTests {
 
@@ -317,6 +319,32 @@ void pathExtension() {
 		assertThat(predicate.test(request)).isFalse();
 	}
 
+	@Test
+	void pathExtensionPredicate() {
+		List<String> extensions = List.of("foo", "bar");
+		RequestPredicate predicate = RequestPredicates.pathExtension(extensions::contains);
+
+		URI uri = URI.create("https://localhost/file.foo");
+		MockServerHttpRequest mockRequest = MockServerHttpRequest.method(HttpMethod.GET, uri).build();
+		ServerRequest request = new DefaultServerRequest(MockServerWebExchange.from(mockRequest), Collections.emptyList());
+		assertThat(predicate.test(request)).isTrue();
+
+		uri = URI.create("https://localhost/file.bar");
+		mockRequest = MockServerHttpRequest.method(HttpMethod.GET, uri).build();
+		request = new DefaultServerRequest(MockServerWebExchange.from(mockRequest), Collections.emptyList());
+		assertThat(predicate.test(request)).isTrue();
+
+		uri = URI.create("https://localhost/file");
+		mockRequest = MockServerHttpRequest.method(HttpMethod.GET, uri).build();
+		request = new DefaultServerRequest(MockServerWebExchange.from(mockRequest), Collections.emptyList());
+		assertThat(predicate.test(request)).isFalse();
+
+		uri = URI.create("https://localhost/file.baz");
+		mockRequest = MockServerHttpRequest.method(HttpMethod.GET, uri).build();
+		request = new DefaultServerRequest(MockServerWebExchange.from(mockRequest), Collections.emptyList());
+		assertThat(predicate.test(request)).isFalse();
+	}
+
 	@Test
 	void queryParam() {
 		MockServerHttpRequest mockRequest = MockServerHttpRequest.get("https://example.com")

spring-webmvc/src/main/java/org/springframework/web/servlet/function/RequestPredicates.java

@@ -841,7 +841,7 @@ public PathExtensionPredicate(String extension) {
 		@Override
 		public boolean test(ServerRequest request) {
 			String pathExtension = UriUtils.extractFileExtension(request.path());
-			return this.extensionPredicate.test(pathExtension);
+			return (pathExtension != null && this.extensionPredicate.test(pathExtension));
 		}
 
 		@Override

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 @@
 
 /**
  * @author Arjen Poutsma
+ * @author Sebastien Deleuze
  */
 class RequestPredicatesTests {
 
@@ -232,6 +234,18 @@ void pathExtension() {
 		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