code: private static String getDbValue(List<DCField> dcFields) {
          if (dcFields.size() == 0) {
              return null;
          }
          StringBuilder out = new StringBuilder(64 * dcFields.size());
  
          for (DCField dcField : dcFields) {
              out.append(' ');
              out.append(dcField.getValue().toLowerCase());
          }
          out.append(" .");
          return out.toString();
      }
docs: Get the string that should be inserted for a repeating-value column,
  given a list of values. Turn each value to lowercase and separate them
  all by space characters. If the list is empty, return null.
  
  @param dcFields
  a list of dublin core values
  @return String the string to insert