UK Contractual Enrolment - bug in fast formula?

Summary:

The docs for contractual enrolment suggest that returning QPS_ID=0 means an employee is not entitled to be contractually enrolled. But doing this generates a fatal error.

Content (please ensure you mask any confidential information):

For contractual enrolment, the documentation says you can provide a "Pension Scheme Formula" - "Predefined fast formula, using naming convention %CONTRACTUAL PENSION%, which returns the variable QPS_ID with the ELEMENT_TYPE_ID of the pension scheme. If a value other than zero is returned, the employee is eligible to join the scheme and enrolled accordingly."

That clearly suggests that a non-zero value means they are enrolled, and by implication a zero value means that they are not.