https://mongodb.github.io/mongo-csharp-driver/3.6.0/api/MongoDB.Bson/MongoDB.Bson.BsonMinKey.html
Class BsonMinKey | MongoDB CSharp Driver API Reference
classmongodbcsharpdriverapi
https://mongodb.github.io/mongo-csharp-driver/2.3/apidocs/html/M_MongoDB_Bson_BsonMinKey_ToString.htm
BsonMinKey.ToString Method
Returns a string representation of the value.
tostringmethod