You may get WELD-000409: Observer method for container lifecycle event can only…​ if using such a lambda in an extension or even WELD-001408 Unsatisfied dependencies for type…​ if using such a lambda in a regular observer and the lambda is using more references (i.e. not only event/disposed parameter) - these are also the method parameters of the synthetic method, and in CDI these additional parameters are injection points.