code: private static List<String> resolveFields(final Iterable<? extends String> fields) {
          final List<String> fieldList = new ArrayList<String>();
  
          for (final String field : fields) {
              Validate.isTrue(StringUtils.isNotBlank(field), "One of the specified fields was blank");
              fieldList.add(field.trim());
          }
  
          return fieldList;
      }
docs: Private helper method for setting the field names. It converts colons to underscores and removes any blanks or
  excess whitespace. Instances are immutable so this method cannot be made public.
  
  @param fields A non-null Iterable of field names.