Must contain at least 1 request. (Parameter 'requests')

It's an error to call BulkWrite with an empty list of requests, and BulkWrite will throw an exception if it is called with an empty list. You can easily replicate it using  following code:

var requests = Enumerable.Empty<WriteModel<C>>();
collection.BulkWrite(requests);

It will throw following run time exception:

System.ArgumentException: Must contain at least 1 request.
Parameter name: requests
   at MongoDB.Driver.MongoCollectionImpl`1.BulkWrite(IEnumerable`1 requests, BulkWriteOptions options, CancellationToken cancellationToken) in C:\work\rstam\mongo-csharp-driver\src\MongoDB.Driver\MongoCollectionImpl.cs:line 151
   at TestCSharp1956.Program.Main(String[] args) in C:\projects\TestCSharp1956\TestCSharp1956\Program.cs:line 27