Ignore nonexistent default-destroy-method in XML config

Prior to this commit, DisposableBeanAdapter attempted to invoke a
configured default-destroy-method on every bean, including beans that
do not declare the named destroy method, resulting in a
NullPointerException being thrown and logged at WARN level.

This commit addresses this by effectively ignoring any nonexistent
destroy method.

Closes gh-30301

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

@@ -236,9 +236,11 @@ class DisposableBeanAdapter implements DisposableBean, Runnable, Serializable {
 		}
 		else if (this.destroyMethods != null) {
 			for (Method destroyMethod : this.destroyMethods) {
+				if (destroyMethod != null) {
 					invokeCustomDestroyMethod(destroyMethod);
 				}
 			}
+		}
 		else if (this.destroyMethodNames != null) {
 			for (String destroyMethodName: this.destroyMethodNames) {
 				Method destroyMethod = determineDestroyMethod(destroyMethodName);