arangosh> db.test.ensureIndex({ type: "skiplist", fields: [ "a[*]" ] }); { "deduplicate" : true, "fields" : [ "a[*]" ], "id" : "test/111712", "isNewlyCreated" : true, "sparse" : false, "type" : "skiplist", "unique" : false, "code" : 201 } arangosh> db.test.save({ a : [ 1, 2 ] }); { "_id" : "test/111715", "_key" : "111715", "_rev" : "_YYClXa---_" } arangosh> db.test.save({ a : [ 1, 3 ] }); { "_id" : "test/111719", "_key" : "111719", "_rev" : "_YYClXaC--_" } arangosh> db.test.save({ a : null }); { "_id" : "test/111722", "_key" : "111722", "_rev" : "_YYClXaC--B" }