Formula: Show Exception in cell

[tennox]

Describe the problem to be solved

In case e.g. a cell the formula depends on is empty, I raise an exception:

if $End is None:
  raise Exception( "End missing")
($End - $Start).total_seconds() / 3600

But the cell just shows:

(It shows the exception name when I double-click into the formula editor)

Describe the solution you would like

I'd love to see the exception message in the cell (instead of the word "Exception" - which is already apparent by the cell being red, imho)

I've also considered returning a literal string instead of an exception, but then downstream formulas result in an opaque type error instead of the clear error message.