arangosh> db.test.ensureIndex({ type: "skiplist", fields: [ "a[*]" ] }); { "deduplicate" : true, "fields" : [ "a[*]" ], "id" : "test/15347", "isNewlyCreated" : true, "sparse" : false, "type" : "skiplist", "unique" : false, "code" : 201 } arangosh> db.test.save({ a : [ 1, 2 ] }); { "_id" : "test/15350", "_key" : "15350", "_rev" : "_VRerCHm---" } arangosh> db.test.save({ a : [ 1, 3 ] }); { "_id" : "test/15354", "_key" : "15354", "_rev" : "_VRerCHq---" } arangosh> db.test.save({ a : null }); { "_id" : "test/15357", "_key" : "15357", "_rev" : "_VRerCHq--_" }