Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{"key":null},{"key":""},{"A":"a"}]
Query
db.collection.find({},{key:1,status:{$cond:{if:{$in:["$key",["",null]]},then:[],else:{$ifNull:["$key",[]]}}}})
Result