cff: Add checks for value types

mentioned in merge request !329 (closed)

mentioned in merge request !330 (closed)

mentioned in merge request !331 (closed)

mentioned in merge request !332 (closed)

mentioned in merge request !333 (closed)

mentioned in merge request !334 (closed)

mentioned in merge request !335 (closed)

mentioned in merge request !336 (closed)

mentioned in merge request !337 (closed)