Excel_UI: Excelsheets with Datasets fail to open

[IsakNaslundBh]

Description:

If a dataset is existing as a formula in excel sheets, it fails to open due to crashing on

Excel_UI/Excel_UI/Addin/AddIn_Formulas.cs

Line 154 in 8ce7467

if (!enumType.IsEnum)

with a null reference exception, due to datasets selected item being a string, not a type.

Steps to reproduce:

Add a dataset to an excel sheet. Save and open excel

Expected behaviour:

For load not to crash when a dataset is present somewhere in the sheet.

[FraserGreenroyd]

@IsakNaslundBh is this the same as #338 ?

[IsakNaslundBh]

No, do not think so. Think this was due to the fix added in #364 where DatasetCallers are passed to the UpdateEnum method, and then when SelectedItem is extracted a string is returned, not type, leading to a null reference exception on line 154 linked above.

Added double protection against it in the linked PR.

Not sure what #338 is about really.