[{"_id":"1","field":{"value":"test"}},{"_id":"2","field":{"value":""}},{"_id":"3","field":{"value":null}},{"_id":"4","field":{}}]

db.collection.aggregate([{"$addFields":{"resValue":{"$cond":{"if":{$eq:[{"$ifNull":["$field.value",""]},""]},"then":"No Data","else":"$field.value"}}}}])