They worked in my simple, void test example

The Optional annotation is parameter, not type bound

WIP: Not really tested and contains RuntimeExceptions that I used for testing
WIP: Not all possible return types covered
WIP: Not really clear which order/priority some statement contents should be checked
WIP: Not dealing with type mismatches or one branch returning something a subclass of the other branch's return type

E.g. IIngredient has a method that accepts an IItemStack, which is a sub-interface

Fairly sure this is an eclipse issue, no problems are reported in idea...
https://bugs.eclipse.org/bugs/show_bug.cgi?id=474593

Threw an exception when an import member could not be found.
Also, the value was not used anywhere

TODO: Verify that the access check is correct

Functional interface wrappers should work now
Implementing a method with a signature differing from the actual one (e.g. when dealing with generics) now creates a proper bridge method
The Java Bytecde compiler used an incorrect method in checkCast
We now no longer use hardcoded 'accept's as method names but whatever the context tells us to.