Follow-up from "Add worker to cache tag signatures"

The following discussion from !211110 should be addressed:

• @vyaklushin started a discussion:

  suggestion (non-blocking): It's unlikely now, but in case of misconfiguration klass_constant can be nil if provided klass is missing. Should we add protection for this case?

  klass_constant = klass.to_s.safe_constantize
  next [] unless klass_constant