Revise use of Objects.requireNonNull()

Historically, we have rarely intentionally thrown a
NullPointerException in the Spring Framework. Instead, we prefer to
throw either an IllegalArgumentException or IllegalStateException
instead of a NullPointerException.

However, changes to the code in recent times have introduced the use of
Objects.requireNonNull(Object) which throws a NullPointerException
without an explicit error message.

The latter ends up providing less context than a NullPointerException
thrown by the JVM (since Java 14) due to actually de-referencing a
null-pointer. See https://openjdk.org/jeps/358.

In light of that, this commit revises our current use of
Objects.requireNonNull(Object) by removing it or replacing it with
Assert.notNull().

However, we still use Objects.requireNonNull(T, String) in a few places
where we are required to throw a NullPointerException in order to
comply with a third-party contract such as Reactive Streams.

Closes gh-32430

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/AbstractNamedValueArgumentResolver.java

@@ -18,7 +18,6 @@ package org.springframework.web.reactive.result.method.annotation;
 
 import java.lang.reflect.Method;
 import java.util.Map;
-import java.util.Objects;
 import java.util.concurrent.ConcurrentHashMap;
 
 import kotlin.reflect.KFunction;
@@ -37,6 +36,7 @@ import org.springframework.core.MethodParameter;
 import org.springframework.core.ReactiveAdapterRegistry;
 import org.springframework.lang.Nullable;
 import org.springframework.ui.Model;
+import org.springframework.util.Assert;
 import org.springframework.web.bind.WebDataBinder;
 import org.springframework.web.bind.annotation.ValueConstants;
 import org.springframework.web.reactive.BindingContext;
@@ -334,7 +334,8 @@ public abstract class AbstractNamedValueArgumentResolver extends HandlerMethodAr
 		 * or an optional parameter (with a default value in the Kotlin declaration).
 		 */
 		public static boolean hasDefaultValue(MethodParameter parameter) {
-			Method method = Objects.requireNonNull(parameter.getMethod());
+			Method method = parameter.getMethod();
+			Assert.notNull(method, () -> "Retrieved null method from MethodParameter: " + parameter);
 			KFunction<?> function = ReflectJvmMapping.getKotlinFunction(method);
 			if (function != null) {
 				int index = 0;