Application fails to start if migration script location folder is empty

[nilskuhn]

Observed behaviour:

If we configure a migration script location in Springs application.yml, which doesn't contain any migration scripts yet, application doesn't start due to the following error:

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-03-08 13:30:26,966 ERROR [main] o.s.b.SpringApplication:837 Application run failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'elasticsearchEvolutionInitializer' defined in class path resource [com/senacor/elasticsearch/evolution/spring/boot/starter/autoconfigure/ElasticsearchEvolutionAutoConfiguration.class]: Invocation of init method failed; nested exception is org.reflections.ReflectionsException: Scanner ResourcesScanner was not configured
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1794)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:594)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516)
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:897)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:879)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551)
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:143)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:758)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:750)
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:405)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1237)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
	at <app-package>.MainKt.main(Main.kt:15)
Caused by: org.reflections.ReflectionsException: Scanner ResourcesScanner was not configured
	at org.reflections.Store.get(Store.java:39)
	at org.reflections.Store.get(Store.java:61)
	at org.reflections.Store.get(Store.java:56)
	at org.reflections.Reflections.getResources(Reflections.java:564)
	at com.senacor.elasticsearch.evolution.core.internal.migration.input.MigrationScriptReaderImpl.readScriptsFromClassPath(MigrationScriptReaderImpl.java:126)
	at com.senacor.elasticsearch.evolution.core.internal.migration.input.MigrationScriptReaderImpl.readFromLocation(MigrationScriptReaderImpl.java:88)
	at com.senacor.elasticsearch.evolution.core.internal.migration.input.MigrationScriptReaderImpl.lambda$read$0(MigrationScriptReaderImpl.java:68)
	at java.base/java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:271)
	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1655)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)
	at com.senacor.elasticsearch.evolution.core.internal.migration.input.MigrationScriptReaderImpl.read(MigrationScriptReaderImpl.java:75)
	at com.senacor.elasticsearch.evolution.core.ElasticsearchEvolution.migrate(ElasticsearchEvolution.java:101)
	at com.senacor.elasticsearch.evolution.spring.boot.starter.autoconfigure.ElasticsearchEvolutionInitializer.afterPropertiesSet(ElasticsearchEvolutionInitializer.java:29)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1853)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1790)
	... 17 common frames omitted

Process finished with exit code 1

This is the part of the configuration which lets the application fail to start:

spring:
  elasticsearch:
    evolution:
      locations:
        - classpath:es/migration/app-name

Without the locations part, the app starts correctly.

Expected behaviour:

The application should start without any errors, if we configure an empty folder as one of the migration script locations.

[xtermi2]

Hi @nilskuhn,

thanks for reporting this bug. I can reproduce this Issue and will provied shortly a fixed version.
In the meanwhile you can quick fix this by placeing a file, e.g. a readme.md or any other file in the location directory.

Best Regards
Andi