Avoid NPE when @SpringBootConfiguration not found in test

See gh-33371

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/context/SpringBootTestContextBootstrapper.java

@@ -244,8 +244,6 @@ protected Class<?>[] getOrFindConfigurationClasses(MergedContextConfiguration me
 			return classes;
 		}
 		Class<?> found = findConfigurationClass(mergedConfig.getTestClass());
-		Assert.state(found != null, "Unable to find a @SpringBootConfiguration, you need to use "
-				+ "@ContextConfiguration or @SpringBootTest(classes=...) with your test");
 		logger.info("Found @SpringBootConfiguration " + found.getName() + " for test " + mergedConfig.getTestClass());
 		return merge(found, classes);
 	}
@@ -258,6 +256,8 @@ private Class<?> findConfigurationClass(Class<?> testClass) {
 			return ClassUtils.resolveClassName(foundClassName, testClass.getClassLoader());
 		}
 		Class<?> found = new AnnotatedClassFinder(SpringBootConfiguration.class).findFromClass(testClass);
+		Assert.state(found != null, "Unable to find a @SpringBootConfiguration, you need to use "
+				+ "@ContextConfiguration or @SpringBootTest(classes=...) with your test");
 		this.aotTestAttributes.setAttribute(propertyName, found.getName());
 		return found;
 	}