code: @Override
      protected String doBase(String name, Object value) {
          if (value instanceof Boolean) {
              return (Boolean) value ? TRUE : FALSE;
          } else if (value instanceof String) {
              return base(name, (String) value);
          }
          throw new IndexException("Field '{}' requires a boolean, but found '{}'", name, value);
      }
docs: {@inheritDoc}