title: AsyncStorage retuning null not get Item
body: <p>asyncStorage getItem. the console is showing the value is null . how to solve this ?    </p>
  
  <pre><code> async componentWillMount(){
     await AsyncStorage.setItem("user", {"name": "nahid" , "id": "2323"})
  
    }
  
    async componentDidMount() {
     var res = await AsyncStorage.getItem('user')
     console.log("sdds",res)
    }
  </code></pre>