Map<String, List<Locale>> map = Collections.singletonMap("Foo", Arrays.asList(Locale.US));
DBObject result = new BasicDBObject();
converter.write(map, result);
assertThat(result.containsField("Foo"), is(true));
assertThat(result.get("Foo"), is(notNullValue()));
assertThat(result.get("Foo"), is(instanceOf(BasicDBList.class)));
BasicDBList list = (BasicDBList) result.get("Foo");