Since SPR-17034, the core container now behaves a bit differently when
dealing with `null` beans.
Given a `null` `HandlerMapping` bean named "resourceHandlerMapping":
* `context.getBean("resourceHandlerMapping", HandlerMapping.class)`
still returns a `NullBean`
* `ListableBeanFactory.getBeansOfType` will return a Map of all existing
beans, not including the `null` ones as values of the map.
Closes gh-13760
9b60eef0e2