Translate NullBean result to null for lookup method with bean name

Closes gh-25806

Author: jhoeller

spring-beans/src/main/java/org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java

@@ -1134,9 +1134,10 @@ protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd
 	 * @see #getObjectForBeanInstance
 	 */
 	protected BeanWrapper obtainFromSupplier(Supplier<?> instanceSupplier, String beanName) {
+		Object instance;
+
 		String outerBean = this.currentlyCreatedBean.get();
 		this.currentlyCreatedBean.set(beanName);
-		Object instance;
 		try {
 			instance = instanceSupplier.get();
 		}
@@ -1148,6 +1149,10 @@ protected BeanWrapper obtainFromSupplier(Supplier<?> instanceSupplier, String be
 				this.currentlyCreatedBean.remove();
 			}
 		}
+
+		if (instance == null) {
+			instance = new NullBean();
+		}
 		BeanWrapper bw = new BeanWrapperImpl(instance);
 		initBeanWrapper(bw);
 		return bw;

spring-beans/src/main/java/org/springframework/beans/factory/support/CglibSubclassingInstantiationStrategy.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -286,8 +286,10 @@ public Object intercept(Object obj, Method method, Object[] args, MethodProxy mp
 			Assert.state(lo != null, "LookupOverride not found");
 			Object[] argsToUse = (args.length > 0 ? args : null);  // if no-arg, don't insist on args at all
 			if (StringUtils.hasText(lo.getBeanName())) {
-				return (argsToUse != null ? this.owner.getBean(lo.getBeanName(), argsToUse) :
+				Object bean = (argsToUse != null ? this.owner.getBean(lo.getBeanName(), argsToUse) :
 						this.owner.getBean(lo.getBeanName()));
+				// Detect package-protected NullBean instance through equals(null) check
+				return (bean.equals(null) ? null : bean);
 			}
 			else {
 				return (argsToUse != null ? this.owner.getBean(method.getReturnType(), argsToUse) :

spring-beans/src/test/java/org/springframework/beans/factory/annotation/LookupAnnotationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@
 import org.junit.Before;
 import org.junit.Test;
 
+import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
 import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.tests.sample.beans.TestBean;
@@ -110,10 +111,23 @@ public void testWithEarlyInjection() {
 		assertSame(bean, beanFactory.getBean(BeanConsumer.class).abstractBean);
 	}
 
+	@Test  // gh-25806
+	public void testWithNullBean() {
+		RootBeanDefinition tbd = new RootBeanDefinition(TestBean.class, () -> null);
+		tbd.setScope(BeanDefinition.SCOPE_PROTOTYPE);
+		beanFactory.registerBeanDefinition("testBean", tbd);
+
+		AbstractBean bean = beanFactory.getBean("beanConsumer", BeanConsumer.class).abstractBean;
+		assertNotNull(bean);
+		Object expected = bean.get();
+		assertNull(expected);
+		assertSame(bean, beanFactory.getBean(BeanConsumer.class).abstractBean);
+	}
+
 
 	public static abstract class AbstractBean {
 
-		@Lookup
+		@Lookup("testBean")
 		public abstract TestBean get();
 
 		@Lookup