Support empty file names in UriUtils::extractFileExtension

Closes gh-27639

spring-web/src/main/java/org/springframework/web/util/UriUtils.java

@@ -407,7 +407,7 @@ public abstract class UriUtils {
 		int paramIndex = path.indexOf(';', begin);
 		end = (paramIndex != -1 && paramIndex < end ? paramIndex : end);
 		int extIndex = path.lastIndexOf('.', end);
-		if (extIndex != -1 && extIndex > begin) {
+		if (extIndex != -1 && extIndex >= begin) {
 			return path.substring(extIndex + 1, end);
 		}
 		return null;

spring-web/src/test/java/org/springframework/web/util/UriUtilsTests.java

@@ -133,6 +133,7 @@ public class UriUtilsTests {
 		assertThat(UriUtils.extractFileExtension("/products;q=11/view.html?param=/path/a.do")).isEqualTo("html");
 		assertThat(UriUtils.extractFileExtension("/products;q=11/view.html;r=22?param=/path/a.do")).isEqualTo("html");
 		assertThat(UriUtils.extractFileExtension("/products;q=11/view.html;r=22;s=33?param=/path/a.do")).isEqualTo("html");
+		assertThat(UriUtils.extractFileExtension("/products/.html")).isEqualTo("html");
 	}
 
 }