ArcGIS Pro should enforce NOT NULL attributes in the application, which then forces the user to input a value to satisfy the constraint.
Currently, there’s no user experience in ArcGIS which enforces this contract when attributes are defined as NOT NULL – when a value is not set the value defaults to an empty string or integer. This is invalid behavior and the work arounds are not suitable, using contingent attribute values or an attribute rule to raise an error. This enhancement begins with the application UX to require the user to set a value before applying the edit.