code: function getStringsFromCategories(props, axis) {
    if (!props.categories) {
      return [];
    }
    const categories = getCategories(props, axis);
    const categoryStrings = categories && categories.filter((val) => typeof val === "string");
    return categoryStrings ? Collection.removeUndefined(categoryStrings) : [];
  }
docs: Returns an array of strings from categories for a given axis
  @param {Object} props: the props object
  @param {String} axis: the current axis
  @returns {Array} an array of strings