Can't save constraint rule for identifying null-values

[PatrickLösel]

I am currently trying to set a constraint rule. No NULL values should be allowed for the attributes. I am using the following code for this:

if (IsEmpty($feature.ART))

Return false

If I now want to save this attribute rule, I only get a red field at the beginning of the rule and saving is not possible. No error message is displayed in the log function of the diagnostic monitor.
The data is stored in an ArcGIS Enterprise geodatabase, which was created with ArcGIS Enterprise 11.1 and I am working with ArcGIS Pro 3.2.2.
The only other thing I have noticed is that when opening the “Attribute rules” view, the following error message appears in the diagnostic monitor:

Input feature class not registered as LRS Network.

Input table not registered as LRS Event.