For `@Bean` method that returns `null`, `@Autowired` injects `NullBean` instead of `null` for cached arguments

[qiangyt]

Affects: 5.x

---

See below test case:

import org.testng.annotations.Test;

import org.testng.Assert;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;

public class NullBeanIssue {

    @Test
    public void test_shouldGetNull() {
        var ctx = new AnnotationConfigApplicationContext();
        ctx.register(MyFactoryBean.class);
        ctx.refresh();

        var myBean = ctx.getBean("myBean");

        // expects null because MyFactoryBean.myBean returns null,
        // however, I got a NullBean instance here
        Assert.assertNull(myBean);

        ctx.close();
    }

}

class MyBean {
}

class MyFactoryBean {

    @Bean
    public MyBean myBean() {
        return null; // in real project cases, return value might be null or not null that depends.
    }

}

[quaff]

Have you tried latest version? IIRC this is fixed long long ago.

[quaff]

I can verify injection works fine but get bean doesn't work, tested with v6.0.8.

import static org.assertj.core.api.Assertions.assertThat;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit.jupiter.SpringExtension;

@ContextConfiguration(classes = NullBeanTests.Config.class)
@ExtendWith(SpringExtension.class)
public class NullBeanTests {

	@Autowired
	private String myBean;

	@Test
	void testInjection() { // will pass
		assertThat(myBean).isNull();
	}

	@Test
	public void testGetBean() { // will fail
		try (var ctx = new AnnotationConfigApplicationContext()) {
			ctx.register(Config.class);
			ctx.refresh();
			assertThat(ctx.getBean("myBean")).isNull();
		}
	}

	static class Config {

		@Bean
		public String myBean() {
			return null;
		}

	}
}

[qiangyt]

Have you tried latest version? IIRC this is fixed long long ago.

Not yet tried 6.x, but all 5.x have this issue.

[qiangyt]

Injection works, but applicationContext.getBean() doesn't work. I updated the issue title.

[sbrannen]

@qiangyt, thanks for reporting this.

@quaff, thanks for providing the autowiring/injection test case.

Interestingly, it turns out that autowiring does not consistently work either.

Here's a modified version of the combined tests which demonstrates that.

import org.junit.jupiter.api.MethodOrderer.OrderAnnotation;
import org.junit.jupiter.api.Order;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestMethodOrder;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;

import static org.assertj.core.api.Assertions.assertThat;

@SpringJUnitConfig(NullBeanTests.Config.class)
@TestMethodOrder(OrderAnnotation.class)
class NullBeanTests {

	@Autowired
	String myBean;

	@Test
	@Order(1)
	void fieldInjection() {
		assertThat(myBean).isNull();
	}

	@Test
	@Order(2)
	void parameterInjection(@Autowired String myBean) {
		assertThat(myBean).isNull();
	}

	@Test
	@Order(99)
	void getBean() {
		try (var ctx = new AnnotationConfigApplicationContext(Config.class)) {
			Object bean = ctx.getBean("myBean");
			System.err.println(bean != null ? bean.getClass().getName() : null);
			assertThat(bean).isNull();
		}
	}

	// @Configuration
	static class Config {

		@Bean
		String myBean() {
			return null;
		}

	}

}

getBean() always fails.

If you run fieldInjection() or parameterInjection() by itself, each will pass.

If you run the NullBeanTests above unmodified, fieldInjection() will pass but only because it runs first. The other two test methods fail.

If you change the @Order of fieldInjection() to 10, parameterInjection() will pass and fieldInjection() will fail.

If you change the @Order of getBean() to 0, all three tests will fail.

If you only change the NullBeanTests above so that String myBean field is annotated with @Autowired(required = false), then fieldInjection() and parameterInjection() will both pass.

So, there is something interesting going on here, and it's definitely a bug (and possibly a regression).

We'll look into it.