arangosh> db.test.ensureIndex({ type: "hash", fields: [ "a[*]" ] }); { "id" : "test/15104", "type" : "hash", "fields" : [ "a[*]" ], "selectivityEstimate" : 1, "unique" : false, "sparse" : false, "isNewlyCreated" : true, "code" : 201 } arangosh> db.test.save({ a : [ 1, 2 ] }); { "_id" : "test/15107", "_key" : "15107", "_rev" : "_U-_q2tu---" } arangosh> db.test.save({ a : [ 1, 3 ] }); { "_id" : "test/15111", "_key" : "15111", "_rev" : "_U-_q2ty---" } arangosh> db.test.save({ a : null }); { "_id" : "test/15114", "_key" : "15114", "_rev" : "_U-_q2ty--_" }