GH-1341 - Avoid potential NullPointerException in annotation lookup for JavaPackage.

We now explicitly filter null values in the annotation lookup that could stem from the initial filtering based on the sole presence of the annotation and the subsequent step trying to load that annotation.

Author: odrotbohm

spring-modulith-core/src/main/java/org/springframework/modulith/core/JavaPackage.java

@@ -24,6 +24,7 @@
 import java.util.Collection;
 import java.util.Comparator;
 import java.util.Iterator;
+import java.util.List;
 import java.util.Map.Entry;
 import java.util.Objects;
 import java.util.Optional;
@@ -36,6 +37,7 @@
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
+import org.jspecify.annotations.NonNull;
 import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.modulith.PackageInfo;
 import org.springframework.util.Assert;
@@ -407,11 +409,12 @@ public <A extends Annotation> Optional<A> findAnnotation(Class<A> annotationType
 
 		var isPackageInfo = have(simpleName(PACKAGE_INFO_NAME)).or(are(metaAnnotatedWith(PackageInfo.class)));
 
-		var annotatedTypes = toSingle().classes
+		List<@NonNull A> annotatedTypes = toSingle().classes
 				.that(isPackageInfo.and(are(metaAnnotatedWith(annotationType))))
 				.stream()
 				.map(JavaClass::reflect)
 				.map(it -> AnnotatedElementUtils.findMergedAnnotation(it, annotationType))
+				.filter(it -> it != null)
 				.toList();
 
 		if (annotatedTypes.size() > 1) {