1. propTypes 空陣列報undefined Warning

舉例來說：

import React from 'react';
import { Breadcrumb, Icon } from 'antd';
import PropTypes from 'prop-types'

const BreadcrumbBlock = ({ paths }) => {

  const items = paths.map( (path, index) => (
      <Breadcrumb.Item key={index+1}>
        <span>{path}</span>
      </Breadcrumb.Item>
  ))
 
;

  return (
    <Breadcrumb separator='>'>
      <Breadcrumb.Item key="0">
        <Icon type="home"/>
      </Breadcrumb.Item>
      {items}
    </Breadcrumb>
  );
}

Breadcrumb.propTypes = {
  paths: PropTypes.array.isRequired
}

export default BreadcrumbBlock;

如果針對paths ＝［］，則console會報warning：指示paths 的值是undefined，原來如果設定isRequired屬性，空值也預設是undefined，去掉後一切正常。

Breadcrumb.propTypes = {
  paths: PropTypes.array
}