Fixed the check constraint for the 'period' param and added some comments to explain the intention of the check logic.
Fixed the check constraint for the 'period' param and added some comments to explain the intention of the check logic.


Former-commit-id: eb9fe7177498d649a145bf3191de6a58ea791fd5 [formerly 14a594cc88170d4f6ddbfc7b802b4078cd28e543]
Former-commit-id: 79f46c07e1edc2e56549bb1c0336e335c2dd80d5
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine