TypeError: Cannot read properties of null (reading ‘username‘)

redux-logger.js:408 error TypeError: Cannot read properties of null (reading ‘username’) at ArticleItem. (articleItem.js:102:1) at Array.map () at ArticleItem.render (articleItem.js:47:1) at finishClassComponent (react-dom.development.js:17098:1) at updateClassComponent (react-dom.development.js:17051:1) at beginWork (react-dom.development.js:18513:1) at HTMLUnknownElement.callCallback (react-dom.development.js:189:1) at Object.invokeGuardedCallbackDev (react-dom.development.js:238:1) at invokeGuardedCallback (react-dom.development.js:291:1) at beginWork$1 (react-dom.development.js:23055:1) at performUnitOfWork (react-dom.development.js:22022:1) at workLoopSync (react-dom.development.js:21995:1) at performSyncWorkOnRoot (react-dom.development.js:21613:1) at react-dom.development.js:11131:1 at unstable_runWithPriority (scheduler.development.js:659:1) at runWithPriority$1 (react-dom.development.js:11077:1) at flushSyncCallbackQueueImpl (react-dom.development.js:11126:1) at flushSyncCallbackQueue (react-dom.development.js:11114:1) at scheduleUpdateOnFiber (react-dom.development.js:21056:1) at Object.enqueueSetState (react-dom.development.js:12676:1) at push…/node_modules/_react@16.14.0@react/cjs/react.development.js.Component.setState (react.development.js:464:1) at Connect.onStateChange (connectAdvanced.js:205:1) at dispatch (redux.js:298:1) at redux-logger.js:458:1 at index.js:20:1 at dispatch (redux.js:694:1) at action.js:54:1

TypeError: Cannot read properties of null (reading ‘username’)

{
          
   
     v.author&&
  v.user&&    //  我这里是这句不能不加 ，必须  判断 v.user不为空，才能去获取  v.user.username
     v.author.length > 0 && v.author != None ?
        <Link to={
          
   "/user/" + v.user.username} className="author-media-avatar">
            <img src={
          
   v.user.avatar} alt=""/>
        </Link>
        :
        null
                        }