The previous implementations resulted in an overload being hidden by one
without a default parameter, making it unclear which method was being
called. For example, consider the following signatures:
public MultipartItem(string content, string contenttype = null, string name = null, string filename = null)
public MultipartItem(string contenttype, string name = null, string filename = null)
From https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/named-and-optional-arguments,
> If two candidates are judged to be equally good, preference goes to a
> candidate that does not have optional parameters for which arguments
> were omitted in the call. This is a consequence of a general preference
> in overload resolution for candidates that have fewer parameters.
Kenneth Skovhede