When using CompileStatic and groovy 2.5.0, type checking appears wrong with [Guava's Multimap.asMap |https://google.github.io/guava/releases/25.1-jre/api/docs/com/google/common/collect/ListMultimap.html#asMap--] method. Return type from that method is Map<K, Collection<V>>, but attempting to assign to a variable of that type results in the error message:
Incompatible generic argument types. Cannot assign java.util.Map <K, V> to: java.util.Map <K, Collection>
This previously worked fine with Groovy 2.4.15. Adding an explicit cast to the asMap() call appears to work around the error.
Here is a small script demonstrating the problem: