in core/src/main/scala/com/gu/marley/AvroSerialisable.scala [89:92]
override def read(x: Any): collection.Map[String,V] =
x.asInstanceOf[java.util.Map[Any,Any]].asScala.map {
case (k, v) => (StringSerialisable.read(k), wv.read(v))
}