Fix "Allow optional directories without sub-directories"

Fix the update to `resolvePatternEmptyDirectories` introduced in
commit 01dd68e29e which was incorrectly checking `isOptional`.

See gh-26677

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/config/StandardConfigDataLocationResolver.java

@@ -267,7 +267,7 @@ public class StandardConfigDataLocationResolver
 	private Set<StandardConfigDataResource> resolvePatternEmptyDirectories(StandardConfigDataReference reference) {
 		Resource[] subdirectories = this.resourceLoader.getResources(reference.getDirectory(), ResourceType.DIRECTORY);
 		ConfigDataLocation location = reference.getConfigDataLocation();
-		if (location.isOptional() && ObjectUtils.isEmpty(subdirectories)) {
+		if (!location.isOptional() && ObjectUtils.isEmpty(subdirectories)) {
 			String message = String.format("Config data location '%s' contains no subdirectories", location);
 			throw new ConfigDataLocationNotFoundException(location, message, null);
 		}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/config/ConfigDataEnvironmentPostProcessorIntegrationTests.java

@@ -715,7 +715,8 @@ class ConfigDataEnvironmentPostProcessorIntegrationTests {
 	void runWhenMandatoryWildcardLocationHasNoSubdirectories() {
 		assertThatExceptionOfType(ConfigDataLocationNotFoundException.class).isThrownBy(
 				() -> this.application.run("--spring.config.location=file:src/test/resources/config/0-empty/*/"))
-				.withMessage("Config data location 'file:src/test/resources/config/0-empty/*/' cannot be found");
+				.withMessage(
+						"Config data location 'file:src/test/resources/config/0-empty/*/' contains no subdirectories");
 	}
 
 	@Test