arangosh> db.test.ensureIndex({ type: "hash", fields: [ "a[*]" ] }); { "id" : "test/16013", "type" : "hash", "fields" : [ "a[*]" ], "selectivityEstimate" : 1, "unique" : false, "sparse" : false, "isNewlyCreated" : true, "code" : 201 } arangosh> db.test.save({ a : [ 1, 2 ] }); { "_id" : "test/16016", "_key" : "16016", "_rev" : "16016" } arangosh> db.test.save({ a : [ 1, 3 ] }); { "_id" : "test/16020", "_key" : "16020", "_rev" : "16020" } arangosh> db.test.save({ a : null }); { "_id" : "test/16023", "_key" : "16023", "_rev" : "16023" }