This gives up exhaustiveness checking, for example [in mapReduceTriplets](https://github.com/ankurdave/incubator-spark/blob/574c0d28c2e859a6ed31a2c193cf04e0aa7404a5/graphx/src/main/scala/org/apache/spark/graphx/impl/GraphImpl.scala#L270). Not a big deal, but just in case -- is there another way to get Java compatibility?