How to use the grommet-icons.FormNext function in grommet-icons

lineHeight: 1.45,
        daySize: baseSpacing * 16 / 7 + 'px',
        slideDuration: '0.5s'
      },
      large: {
        fontSize: baseFontSize + fontScale + 'px',
        lineHeight: 1.11,
        daySize: baseSpacing * 32 / 7 + 'px',
        slideDuration: '0.8s'
      },
      icons: {
        previous: _grommetIcons.Previous,
        next: _grommetIcons.Next,
        small: {
          previous: _grommetIcons.FormPrevious,
          next: _grommetIcons.FormNext
        }
      }
    },
    carousel: {
      icons: {
        current: _grommetIcons.Subtract,
        next: _grommetIcons.Next,
        previous: _grommetIcons.Previous
        // color: undefined,
      }
    },
    checkBox: {
      border: {
        color: {
          dark: 'rgba(255, 255, 255, 0.5)',
          light: 'rgba(0, 0, 0, 0.15)'

var MenuButton = function MenuButton(_ref) {
  var label = _ref.label,
      open = _ref.open,
      submenu = _ref.submenu,
      rest = _objectWithoutPropertiesLoose(_ref, ["label", "open", "submenu"]);

  var Icon = open ? _grommetIcons.FormDown : _grommetIcons.FormNext;
  return _react["default"].createElement(_grommet.Button, _extends({
    hoverIndicator: "background"
  }, rest), _react["default"].createElement(_grommet.Box, {
    margin: submenu ? {
      left: 'small'
    } : undefined,
    direction: "row",
    align: "center",
    pad: "xsmall"
  }, _react["default"].createElement(Icon, {
    color: "brand"
  }), _react["default"].createElement(_grommet.Text, {
    size: "small"
  }, label)));
};