Avoid IllegalStateException for unversioned request

Closes gh-35236

Author: rstoyanchev

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

@@ -149,8 +149,7 @@ else if (this.version != null && otherVersion != null) {
 	public void handleMatch(ServerWebExchange exchange) {
 		if (this.version != null && !this.baselineVersion) {
 			Comparable<?> version = exchange.getAttribute(HandlerMapping.API_VERSION_ATTRIBUTE);
-			Assert.state(version != null, "No API version attribute");
-			if (!this.version.equals(version)) {
+			if (version != null && !this.version.equals(version)) {
 				throw new NotAcceptableApiVersionException(version.toString());
 			}
 		}

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

@@ -148,6 +148,17 @@ private void testCompare(String expected, String... versions) {
 		assertThat(list.get(0)).isEqualTo(condition(expected));
 	}
 
+	@Test // gh-35236
+	void noRequestVersion() {
+		MockServerWebExchange exchange = exchange();
+		VersionRequestCondition condition = condition("1.1");
+
+		VersionRequestCondition match = condition.getMatchingCondition(exchange);
+		assertThat(match).isSameAs(condition);
+
+		condition.handleMatch(exchange);
+	}
+
 	private VersionRequestCondition condition(String v) {
 		this.strategy.addSupportedVersion(v.endsWith("+") ? v.substring(0, v.length() - 1) : v);
 		return new VersionRequestCondition(v, this.strategy);

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

@@ -148,8 +148,7 @@ else if (this.version != null && otherVersion != null) {
 	public void handleMatch(HttpServletRequest request) {
 		if (this.version != null && !this.baselineVersion) {
 			Comparable<?> version = (Comparable<?>) request.getAttribute(HandlerMapping.API_VERSION_ATTRIBUTE);
-			Assert.state(version != null, "No API version attribute");
-			if (!this.version.equals(version)) {
+			if (version != null && !this.version.equals(version)) {
 				throw new NotAcceptableApiVersionException(version.toString());
 			}
 		}

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

@@ -146,6 +146,17 @@ private void testCompare(String expected, String... versions) {
 		assertThat(list.get(0)).isEqualTo(condition(expected));
 	}
 
+	@Test // gh-35236
+	void noRequestVersion() {
+		MockHttpServletRequest request = new MockHttpServletRequest("GET", "/path");
+		VersionRequestCondition condition = condition("1.1");
+
+		VersionRequestCondition match = condition.getMatchingCondition(request);
+		assertThat(match).isSameAs(condition);
+
+		condition.handleMatch(request);
+	}
+
 	private VersionRequestCondition condition(String v) {
 		this.strategy.addSupportedVersion(v.endsWith("+") ? v.substring(0, v.length() - 1) : v);
 		return new VersionRequestCondition(v, this.strategy);