Spring Odd behaviour with null bean instance when an alternative autowire candidate is available [SPR-16960]

Dave Syer opened SPR-16960 and commented

Since Spring 5.0 a @Bean can return null and the effect is to leave the bean definition in the registry, but make the value not autowirable. However, if there is another bean of the same type that is not null, it does not become autowirable. Probably it should? The exception from Spring doesn't mention the existence of either bean (the null or the not null one):

norg.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'java.lang.String' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1509)
...

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Affects: 5.0.7

Reference URL: https://github.com/spring-projects/spring-boot/issues/13531

Issue Links: - #21499 Null bean value exception message confusing

Comment From: snicoll

I can no longer reproduce this with a supported version. I am getting:

org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'java.lang.String' available: expected single matching bean but found 2: one,two
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:218) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1395) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1337) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:888) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:791) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:550) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1332) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1162) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:560) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:520) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:326) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:324) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:200) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:973) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:942) ~[spring-context-6.0.11.jar:6.0.11]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:608) ~[spring-context-6.0.11.jar:6.0.11]