Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{a:[{value:1}]},{a:[{value:null}]},{a:[{value:2}]}]
Query
db.collection.find({"$expr":{"$eq":[{"$arrayElemAt":["$a.value",0]},null]}})
Result