About one strange bug (Invalid descriptor)

Hi, all
Since some time I started creating nodes for Dynamo and encounter with some difficulties. Current developer’s guide is great resource but don’t contain all things.
I use VS to create node in C# with ZeroTouchLibrary and last days I was confused why Dynamo want not import code block (or string) to my input_parameter. Below picture with success import after solving problem

Before it I have code’s string that in general will not using Dynamo… but at fact it was used:
public static string ConvertTMerc_RectangleToWGS84(double Revit_X_coord = 0, double Revit_Y_coord = 0, double H = 0.0, string MSK_description_PROJ = null)
Console.OutputEncoding = System.Text.Encoding.UTF8; //Support Unocode-encoding
With that string I got picture below:

In error screnn there are info “Неверный дескриптор” or “Invalid descriptor” and long time I didn’t understanding what was happened until delete all code and test every string up moment when all start working

I hope it info may be helpful smb, because I wasn’t finding any Posts here with tag “descriptor”… as if nobody hadn’t that problem in practice