[{id:1,firstname:"paul",lastname:"pogba",goals:2,},{id:2,firstname:"fred",lastname:"",goals:2,},{id:3,firstname:"",lastname:"rashford",goals:5,},{id:4,firstname:"luke",lastname:"shaw",goals:0,}]

db.collection.aggregate([{$match:{goals:{$gt:0}}},{$group:{_id:null,firstname:{$push:"$firstname"},lastname:{$push:"$lastname"}}},{$project:{_id:0,result:{$filter:{input:{$concatArrays:["$firstname","$lastname"]},cond:{$ne:["$$this",""]}}}}}])