Database
[{_id:ObjectId("61e1312ad435c7124aa883a1"),name:"Brian",languages:"English,Spanish,French"},{_id:ObjectId("52e1312ad435c7124aa883a2"),name:"Max",languages:"English"},{_id:ObjectId("37e1312ad435c7124aa883a9"),name:"Mike",languages:""}]
Query
db.collection.aggregate([{$addFields:{"languages":{$filter:{input:{$split:["$languages",","]},cond:{$gt:[{$strLenCP:"$$this"},0]}}}}}])