arangosh> db.test.ensureIndex({ type: "skiplist", fields: [ "a[*]" ] }); { "deduplicate" : true, "fields" : [ "a[*]" ], "id" : "test/16097", "isNewlyCreated" : true, "sparse" : false, "type" : "skiplist", "unique" : false, "code" : 201 } arangosh> db.test.save({ a : [ 1, 2 ] }); { "_id" : "test/16100", "_key" : "16100", "_rev" : "_WcJRga6--_" } arangosh> db.test.save({ a : [ 1, 3 ] }); { "_id" : "test/16104", "_key" : "16104", "_rev" : "_WcJRgb---_" } arangosh> db.test.save({ a : null }); { "_id" : "test/16107", "_key" : "16107", "_rev" : "_WcJRgb---B" }