Fix IllegalStateException in empty ProducesRequestCondition

When comparing empty ProducesRequestCondition, compareTo would throw an
IllegalStateException if the Accept header was invalid. This commit
fixes that behavior.

Closes gh-29794

spring-webflux/src/main/java/org/springframework/web/reactive/result/condition/ProducesRequestCondition.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -248,6 +248,9 @@ public final class ProducesRequestCondition extends AbstractRequestCondition<Pro
 	 */
 	@Override
 	public int compareTo(ProducesRequestCondition other, ServerWebExchange exchange) {
+		if (this.expressions.isEmpty() && other.expressions.isEmpty()) {
+			return 0;
+		}
 		try {
 			List<MediaType> acceptedMediaTypes = getAcceptedMediaTypes(exchange);
 			for (MediaType acceptedMediaType : acceptedMediaTypes) {

spring-webflux/src/test/java/org/springframework/web/reactive/result/condition/ProducesRequestConditionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -297,6 +297,18 @@ public class ProducesRequestConditionTests {
 		assertThat(result > 0).as("Should have used MediaType.equals(Object) to break the match").isTrue();
 	}
 
+	@Test
+	public void compareEmptyInvalidAccept() {
+		MockServerWebExchange exchange = MockServerWebExchange.from(get("/").header("Accept", "foo"));
+
+		ProducesRequestCondition condition1 = new ProducesRequestCondition();
+		ProducesRequestCondition condition2 = new ProducesRequestCondition();
+
+		int result = condition1.compareTo(condition2, exchange);
+		assertThat(result).isEqualTo(0);
+	}
+
+
 	@Test
 	public void combine() {
 		ProducesRequestCondition condition1 = new ProducesRequestCondition("text/plain");

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/condition/ProducesRequestCondition.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -254,6 +254,9 @@ public final class ProducesRequestCondition extends AbstractRequestCondition<Pro
 	 */
 	@Override
 	public int compareTo(ProducesRequestCondition other, HttpServletRequest request) {
+		if (this.expressions.isEmpty() && other.expressions.isEmpty()) {
+			return 0;
+		}
 		try {
 			List<MediaType> acceptedMediaTypes = getAcceptedMediaTypes(request);
 			for (MediaType acceptedMediaType : acceptedMediaTypes) {

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/condition/ProducesRequestConditionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -309,6 +309,17 @@ public class ProducesRequestConditionTests {
 		assertThat(result > 0).as("Should have used MediaType.equals(Object) to break the match").isTrue();
 	}
 
+	@Test
+	public void compareEmptyInvalidAccept() {
+		HttpServletRequest request = createRequest("foo");
+
+		ProducesRequestCondition condition1 = new ProducesRequestCondition();
+		ProducesRequestCondition condition2 = new ProducesRequestCondition();
+
+		int result = condition1.compareTo(condition2, request);
+		assertThat(result).isEqualTo(0);
+	}
+
 	@Test
 	public void combine() {
 		ProducesRequestCondition condition1 = new ProducesRequestCondition("text/plain");