GH-520 - Early reject invalid ApplicationModules bootstraps.

We now immediately reject the ApplicationModules bootstrap in case the initial scanning of the root packages yield no classes at all.

spring-modulith-integration-test/src/main/java/example/empty/EmptyApplication.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2024 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package example.empty;
+
+import org.springframework.modulith.Modulithic;
+
+/**
+ * @author Oliver Drotbohm
+ */
+@Modulithic
+public class EmptyApplication {
+
+}