As stated in various discussion on JDK8, lambda expressions don't allow to retrieve parameter types by reflection.
As section 10.1 of the spec states:
The event types of the event include all superclasses and interfaces of the runtime class of the event object.
In case of a lambda payload, observer resolution will fails when respecting the rule above since parameter type won't be retrieve from the lambda.
For instance the following code
will triggers an observer for Supplier but not an observer for Supplier<String>.