code: def variant_cv_tissue_site(value)
        # try an NOS suffix variation
        variation = value =~ /, NOS$/ ? value[0...-', NOS'.length] : value + ', NOS'
        SpecimenCharacteristics.tissue_site_controlled_value(variation) rescue nil
      end
docs: Returns the tissue site which adds the 'NOS' suffix to a value without one
   or removes 'NOS' from a value with the suffix.
  
   @return [String, nil] a supported variant of the input value, or nil if none