I just found myself having NULLed [Geom] by accident with a transform command in GUI - and not for the first time.
If [mfd_id] were the default field for transforms my overhasty applies would not be so disastrous because manual edits are blocked with error ' ": Unkown name. ' . I love this convoluted error message in comparison with losing my geometries.
Do you want us to set the target field in the Transform pane to MFD_ID by default? I don't think this would be a good way to protect from accidental misapplications of transforms, that field is frequently writable. But perhaps we can protect from accidental misapplications using other ways. What specific transform did you accidentally launch on the Geom field?
I applied expressions returning strings resulting in <NULL>, not functions. But that probably is not a good hint to capture all unwanted elimination of geoms.
Klaus, I’m very interested in this, but I don’t understand.
Can you give exact steps?
You have a drawing and want to set values of a text field in all selected records. So you go to the transform pan, change tab to Expression and type the text in the control for the formula. It's only '12345' - set scope to 'Restrict to Selection' and than 'Update field'.
Bang! You have forgotten to change the default target field in the grey and inconspicious control on top from [geom] to the field you want to change and thus have nulled all geometries of the selected records. No undo.
Yes, the preview was perfect and did show nothing where the objects should be. But 'nothing' isn't so obvious.
 The question is: is there any good reason to set a geom to null in an expression or formula? I really don't know.
Got in the same trouble few times. For me the best would be to have this top field set to nothing, forcing us to set itin order to avoid this user mistake
Got it, it's the Expression tab. We will try to add some protection there.