Change error type returned to an actual error type

[IsakNaslundBh]

Description:

When something crashes in code executed, might be due to anything really, you generally get ExcelErrorNull returned from the toolkit. This type of error is not recognised as an error by the native =IFERROR( command in Excel.

This can be quite annoying when you want to set up a sheet to be ready to receive data from an adapter or similar, where a simple =IFERROR( do some stuff, "") can be a quite nice way to keep the sheet looking clean without to much hassle.

Would suggest a #VALUE or similar to be returned instead (not sure if there is like `#NULL' or similar that would be an even better fit), basically, something picked up by Excel as being an error.

https://github.com/BHoM/Excel_Toolkit/blob/master/Excel_UI/Addin/AddIn_Converts.cs seem to be the main file handling this from my quick search! :)