code: def default_derived_characteristics
        chrs = specimen_characteristics || return
        pas = chrs.class.nondomain_attributes.reject { |pa| pa == :identifier }
        chrs.copy(pas)
      end
docs: Returns characteristics to use for a derived specimen. The new characteristics is copied from this
   parent specimen's characteristics, without the identifier.
  
   @return [CaTissue::SpecimenCharacteristics, nil] a copy of this Specimen's specimen_characteristics, or nil if none