[{"uuid":"00000000-0000-0000-0000-000000000000","name":"Building1","doors":[{"doorUuid":"11111111-1111-1111-1111-111111111111","creationTime":null},{"doorUuid":"22222222-2222-2222-2222-222222222222","creationTime":1560194908942},{"doorUuid":"33333333-3333-3333-3333-333333333333","creationTime":1560195008942}]}]

db.collection.aggregate([{$unwind:"$doors"},{$match:{"doors.creationTime":{$ne:null}}},{$group:{_id:"$_id",name:{$last:"$name"},uuid:{$last:"$uuid"},doors:{$push:"$doors"}}}])