Database
[{"_id":ObjectId("5e9ecf782980434d78120a49"),"data_kv":[{"k":"U1","v":["","","University","","","of","","","Australia","",""]}]},{"_id":ObjectId("5e9ecf7f2980434d78120a4a"),"data_kv":[{"k":"U2","v":["","","University","of","","","","","Australia","",""]}]},{"_id":ObjectId("5e9ecf8a2980434d78120a4b"),"data_kv":[{"k":"U3","v":["","","University","","","of","","","","Sweden","",""]}]}]
Query
db.collection.aggregate([{$project:{data_kv:{$map:{input:"$data_kv",as:"kv",in:{k:"$$kv.k",v:{$filter:{input:"$$kv.v",cond:{$ne:["$$this",""]}}}}}}}}])