db={users:[{"_id":"abc","calculatedDist":112,"group":1,"location":{"coordinates":[53.23,67.12],"type":"Point"},"name":"abc"},{"_id":"xyz","calculatedDist":13,"group":1,"name":"xyyy"},{"_id":"123","calculatedDist":13,"group":1,"location":{"coordinates":[54.23,67.12],"type":"Point"},"name":"yyy"},{"_id":"rrr","calculatedDist":14,"group":1,"location":{"coordinates":[51.23,64.12],"type":"Point"},"name":"tttt"},{"_id":"mmm","calculatedDist":14,"group":1,"name":"mmmm"}]}

db.users.aggregate([{"$geoNear":{"near":{"type":"Point","coordinates":[53.23,67.12]},"distanceField":"d"}},{"$unionWith":{"coll":"users","pipeline":[{"$match":{"location":null}}]}}])