Fix code generation for null indexed argument value

This commit fixes code generation when an indexed constructor argument
value is null as the method is overloaded and need the value to be
cast to `Object`.

Closes gh-31508

spring-beans/src/test/java/org/springframework/beans/factory/aot/BeanDefinitionPropertiesCodeGeneratorTests.java

@@ -235,6 +235,18 @@ class BeanDefinitionPropertiesCodeGeneratorTests {
 		});
 	}
 
+	@Test
+	void constructorArgumentValuesWhenIndexedNullValue() {
+		this.beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(0, (Object) null);
+		compile((actual, compiled) -> {
+			ConstructorArgumentValues argumentValues = actual.getConstructorArgumentValues();
+			Map<Integer, ValueHolder> values = argumentValues.getIndexedArgumentValues();
+			assertThat(values.get(0)).satisfies(assertValueHolder(null, null, null));
+			assertThat(values).hasSize(1);
+			assertThat(argumentValues.getGenericArgumentValues()).isEmpty();
+		});
+	}
+
 	@Test
 	void constructorArgumentValuesWhenGenericValuesWithName() {
 		this.beanDefinition.getConstructorArgumentValues().addGenericArgumentValue(String.class);
@@ -255,7 +267,9 @@ class BeanDefinitionPropertiesCodeGeneratorTests {
 		});
 	}
 
-	private Consumer<ValueHolder> assertValueHolder(Object value, @Nullable Class<?> type, @Nullable String name) {
+	private Consumer<ValueHolder> assertValueHolder(
+			@Nullable Object value, @Nullable Class<?> type, @Nullable String name) {
+
 		return valueHolder -> {
 			assertThat(valueHolder.getValue()).isEqualTo(value);
 			assertThat(valueHolder.getType()).isEqualTo((type != null ? type.getName() : null));