Allow easy creation of asyncrhonous methods called from bean language.
Proposed solution is to allow such methods to return CompletableFuture.
Such return would automatically be treated as async invocation.
Non-null result will be used as resulting body.
Any async exception will be propagated to proper error handling.
Note that if CompletableFuture would return null, it won't be used as resulting body. Rather resulting body will not be changed. It would help in use cases when processing method just does some work and returns CompletableFuture<Void>.