Springboot autoconfiguration @ConditionalOnClass TypeNotPresentExceptionProxy

Question

Trying to learn Springboot Autoconfiguration.

I created the folowing module with an autoconfiguration class, the idea as indicated is that the bean migrationAutoConfigBeanCreated will be created if the caller app have Flyway library in the claspath:

@Slf4j
@ConditionalOnClass(Flyway.class)
public class MigrationAutoConfiguration {

    @Bean
    public void migrationAutoConfigBeanCreated(){
        log.debug("MigrationAutoConfiguration is called");
    }
}

And it work fine, when the caller module have the Flyway library in it's classpath, the debug log is shown.

The problem is when I try to apply the @ConditionalOnClass only to the bean instead the entire Configuration class, like this:

@Slf4j
public class MigrationAutoConfiguration {

    @Bean
    @ConditionalOnClass(Flyway.class)
    public void migrationAutoConfigBeanCreated(){
        log.debug("MigrationAutoConfiguration is called");
    }
}

I have this error on lunch:

2020-09-30 17:30:21.527 ERROR 26028 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.medkhelifi.tutorials.hwspringautoconfig.migration.MigrationAutoConfiguration': Unexpected exception during bean creation; nested exception is java.lang.ArrayStoreException: sun.reflect.annotation.TypeNotPresentExceptionProxy
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:530) ~[spring-beans-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:879) ~[spring-beans-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:878) ~[spring-context-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.2.1.RELEASE.jar:2.2.1.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) [spring-boot-2.2.1.RELEASE.jar:2.2.1.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.2.1.RELEASE.jar:2.2.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) [spring-boot-2.2.1.RELEASE.jar:2.2.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) [spring-boot-2.2.1.RELEASE.jar:2.2.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) [spring-boot-2.2.1.RELEASE.jar:2.2.1.RELEASE]
    at com.medkhelifi.tutorials.alljava.various.VariousMainApp.main(VariousMainApp.java:9) [classes/:na]

And I don't understand why.

There is my two modules poms:

Autoconfiguration pom:

<dependencies>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
        <optional>true</optional>
    </dependency>
    <dependency>
        <groupId>org.flywaydb</groupId>
        <artifactId>flyway-core</artifactId>
        <optional>true</optional>
    </dependency>
</dependencies>

caller module:

<dependencies>
    <!--            SPRING BOOT                                 -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>org.flywaydb</groupId>
        <artifactId>flyway-core</artifactId>
    </dependency>
    -->
    <!--            AUTOCONFIGURATION                                -->
    <dependency>
        <groupId>com.medkhelifi.tutorials</groupId>
        <artifactId>hello-springboot-starters</artifactId>
    </dependency>
    <!--           DEV TOOLS                                   -->
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
    </dependency>
</dependencies>