Explicit nullability declarations for all AOP Alliance methods

Includes consistent declarations in AOP Alliance related Spring AOP code.

Closes gh-24117

spring-aop/src/main/java/org/aopalliance/intercept/ConstructorInterceptor.java

@@ -16,6 +16,8 @@
 
 package org.aopalliance.intercept;
 
+import javax.annotation.Nonnull;
+
 /**
  * Intercepts the construction of a new object.
  *
@@ -54,6 +56,7 @@ public interface ConstructorInterceptor extends Interceptor  {
 	 * @throws Throwable if the interceptors or the target object
 	 * throws an exception
 	 */
+	@Nonnull
 	Object construct(ConstructorInvocation invocation) throws Throwable;
 
 }

spring-aop/src/main/java/org/aopalliance/intercept/ConstructorInvocation.java

@@ -18,6 +18,8 @@ package org.aopalliance.intercept;
 
 import java.lang.reflect.Constructor;
 
+import javax.annotation.Nonnull;
+
 /**
  * Description of an invocation to a constructor, given to an
  * interceptor upon constructor-call.
@@ -36,6 +38,7 @@ public interface ConstructorInvocation extends Invocation {
 	 * {@link Joinpoint#getStaticPart()} method (same result).
 	 * @return the constructor being called
 	 */
+	@Nonnull
 	Constructor<?> getConstructor();
 
 }

spring-aop/src/main/java/org/aopalliance/intercept/Invocation.java

@@ -16,6 +16,8 @@
 
 package org.aopalliance.intercept;
 
+import javax.annotation.Nonnull;
+
 /**
  * This interface represents an invocation in the program.
  *
@@ -32,6 +34,7 @@ public interface Invocation extends Joinpoint {
 	 * array to change the arguments.
 	 * @return the argument of the invocation
 	 */
+	@Nonnull
 	Object[] getArguments();
 
 }

spring-aop/src/main/java/org/aopalliance/intercept/Joinpoint.java

@@ -18,6 +18,9 @@ package org.aopalliance.intercept;
 
 import java.lang.reflect.AccessibleObject;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
 /**
  * This interface represents a generic runtime joinpoint (in the AOP
  * terminology).
@@ -46,6 +49,7 @@ public interface Joinpoint {
 	 * @return see the children interfaces' proceed definition
 	 * @throws Throwable if the joinpoint throws an exception
 	 */
+	@Nullable
 	Object proceed() throws Throwable;
 
 	/**
@@ -53,6 +57,7 @@ public interface Joinpoint {
 	 * <p>For instance, the target object for an invocation.
 	 * @return the object (can be null if the accessible object is static)
 	 */
+	@Nullable
 	Object getThis();
 
 	/**
@@ -60,6 +65,7 @@ public interface Joinpoint {
 	 * <p>The static part is an accessible object on which a chain of
 	 * interceptors are installed.
 	 */
+	@Nonnull
 	AccessibleObject getStaticPart();
 
 }

spring-aop/src/main/java/org/aopalliance/intercept/MethodInterceptor.java

@@ -16,6 +16,9 @@
 
 package org.aopalliance.intercept;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
 /**
  * Intercepts calls on an interface on its way to the target. These
  * are nested "on top" of the target.
@@ -52,6 +55,7 @@ public interface MethodInterceptor extends Interceptor {
 	 * @throws Throwable if the interceptors or the target object
 	 * throws an exception
 	 */
-	Object invoke(MethodInvocation invocation) throws Throwable;
+	@Nullable
+	Object invoke(@Nonnull MethodInvocation invocation) throws Throwable;
 
 }

spring-aop/src/main/java/org/aopalliance/intercept/MethodInvocation.java

@@ -18,6 +18,8 @@ package org.aopalliance.intercept;
 
 import java.lang.reflect.Method;
 
+import javax.annotation.Nonnull;
+
 /**
  * Description of an invocation to a method, given to an interceptor
  * upon method-call.
@@ -36,6 +38,7 @@ public interface MethodInvocation extends Invocation {
 	 * {@link Joinpoint#getStaticPart()} method (same result).
 	 * @return the method being called
 	 */
+	@Nonnull
 	Method getMethod();
 
 }