Update code regarding null-safety semantics

See gh-30083

spring-aop/src/main/java/org/springframework/aop/framework/autoproxy/target/AbstractBeanFactoryBasedTargetSourceCreator.java

@@ -58,6 +58,7 @@ public abstract class AbstractBeanFactoryBasedTargetSourceCreator
 
 	protected final Log logger = LogFactory.getLog(getClass());
 
+	@Nullable
 	private ConfigurableBeanFactory beanFactory;
 
 	/** Internally used DefaultListableBeanFactory instances, keyed by bean name. */
@@ -76,6 +77,7 @@ public abstract class AbstractBeanFactoryBasedTargetSourceCreator
 	/**
 	 * Return the BeanFactory that this TargetSourceCreators runs in.
 	 */
+	@Nullable
 	protected final BeanFactory getBeanFactory() {
 		return this.beanFactory;
 	}

spring-aop/src/main/java/org/springframework/aop/target/AbstractBeanFactoryBasedTargetSource.java

@@ -24,6 +24,7 @@ import org.apache.commons.logging.LogFactory;
 import org.springframework.aop.TargetSource;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
+import org.springframework.lang.Nullable;
 import org.springframework.util.ObjectUtils;
 
 /**
@@ -169,7 +170,7 @@ public abstract class AbstractBeanFactoryBasedTargetSource implements TargetSour
 
 
 	@Override
-	public boolean equals(Object other) {
+	public boolean equals(@Nullable Object other) {
 		if (this == other) {
 			return true;
 		}

spring-aop/src/main/java/org/springframework/aop/target/EmptyTargetSource.java

@@ -131,7 +131,7 @@ public final class EmptyTargetSource implements TargetSource, Serializable {
 	}
 
 	@Override
-	public boolean equals(Object other) {
+	public boolean equals(@Nullable Object other) {
 		if (this == other) {
 			return true;
 		}

spring-aop/src/main/java/org/springframework/aop/target/HotSwappableTargetSource.java

@@ -19,6 +19,7 @@ package org.springframework.aop.target;
 import java.io.Serializable;
 
 import org.springframework.aop.TargetSource;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -100,7 +101,7 @@ public class HotSwappableTargetSource implements TargetSource, Serializable {
 	 * objects are equal.
 	 */
 	@Override
-	public boolean equals(Object obj) {
+	public boolean equals(@Nullable Object obj) {
 		return (this == obj || (obj instanceof HotSwappableTargetSource that &&
 				this.target.equals(that.target)));
 	}

spring-aop/src/main/java/org/springframework/aop/target/LazyInitTargetSource.java

@@ -65,7 +65,6 @@ public class LazyInitTargetSource extends AbstractBeanFactoryBasedTargetSource {
 
 
 	@Override
-	@Nullable
 	public synchronized Object getTarget() throws BeansException {
 		if (this.target == null) {
 			this.target = getBeanFactory().getBean(getTargetBeanName());

spring-aop/src/main/java/org/springframework/aop/target/SingletonTargetSource.java

@@ -19,6 +19,7 @@ package org.springframework.aop.target;
 import java.io.Serializable;
 
 import org.springframework.aop.TargetSource;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 
@@ -82,7 +83,7 @@ public class SingletonTargetSource implements TargetSource, Serializable {
 	 * targets or the targets are equal.
 	 */
 	@Override
-	public boolean equals(Object other) {
+	public boolean equals(@Nullable Object other) {
 		if (this == other) {
 			return true;
 		}