[{"type":"1.2.3"},{"type":"1.2.3"}]

db.collection.aggregate([{"$facet":{"results":[{$match:{"type":"1.2.3"}},{$group:{_id:{$ifNull:["$type",0]},count:{$sum:1}}}]}},{"$replaceRoot":{"newRoot":{"$cond":{"if":{$gt:[{"$size":"$results"},0]},"then":"$$ROOT","else":{"results":[{"_id":"1.2.3","count":0}]}}}}},{"$unwind":"$results"},{"$replaceRoot":{"newRoot":"$results"}}])