if (!(/,$/u).test(preceedingSubfield.value)) {
        if (!(/^[[(]/u).test(currentSubfield.value)) { // eslint-disable-line functional/no-conditional-statements
          const nextValue = `${preceedingSubfield.value},`;
          debug(`Updated subfield ${preceedingSubfield.code} from '${preceedingSubfield.value}' to '${nextValue}'`);
          preceedingSubfield.value = nextValue; // eslint-disable-line functional/immutable-data