Fix on SplitFullName.

src/RhinoInside.Revit.External/DB/Extensions/Category.cs

@@ -77,7 +77,7 @@ internal static string SplitFullName(string fullName, out string parent)
       else
       {
         var index = fullName.IndexOf(CS);
-        parent = fullName.Substring(0, index);
+        parent = index < 0 ? string.Empty : fullName.Substring(0, index);
         return fullName.Substring(index + 1, fullName.Length - index - 1);
       }
     }