The issue was found here:
https://github.com/openjdk/jdk/pull/24692#discussion_r2089545502

AWTEventListener and AWTEventListenerProxy are public classes and there's no assertion that EventListenerProxy.getListener() will always return a non-null value. So removeAWTEventListener method should fetch the listener from the proxy and check it for null similar to how it is implemented in addAWTEventListener. Currently, it works fine because we never insert null values into the map. so it is just a code clarification.