System.TypeLoadException.SetMessageField C# (CSharp) Method

        private void SetMessageField()
        {
            if (_message == null) {
                if ((ClassName == null) &&
                    (ResourceId == 0))
                    _message = Environment.GetResourceString("Arg_TypeLoadException");

                else {
                    if (AssemblyName == null)
                        AssemblyName = Environment.GetResourceString("IO_UnknownFileName");
                    if (ClassName == null)
                        ClassName = Environment.GetResourceString("IO_UnknownFileName");

                    _message = String.Format(CultureInfo.CurrentCulture, GetTypeLoadExceptionMessage(ResourceId), ClassName, AssemblyName, MessageArg);
                }
            }
        }