Describe the bug
The nullability inference seems not to understand De Morgans's laws.

To Reproduce
Assuming there is at least one row in systemuser with a value for fullname and a nickname that is NULL.

select nickname from systemuser
where NOT (fullname is null and nickname is null) 

Produces error:

Column 'nickname' does not allow DBNull.Value.
Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints.

Expected behavior

The equivalent:

select nickname from systemuser
where fullname is not null OR nickname is not null

Works fine.

Environment (please complete the following information):

• SQL 4 CDS edition: XrmToolBox
• Results of SELECT @@VERSION:
  Microsoft Dataverse - 9.2.25051.174
  SQL 4 CDS - 9.6.1.0
  May 02 2025 16:58:10
  Copyright © 2020 - 2025 Mark Carrington