Steps to reproduce

Define a multibinding interface Foo, map no implementations, try to inject Set<Foo> somewhere.

Expected results

Empty set injected

Actual results

Guice injection failure.

Development notes

This happens due to "lazy" registration of multi-binding interfaces: we invoke Guice.newSetMultibinder() only while registering an actual implementation of an interface. This is all due to the lack of specific syntax that would let us declare the presence of such interface itself. The attached PR suggests to add such syntax.