title: Why appear this error when I delete all string to empty in react-native TextInput components?
body: <p>I have a react-native code in the below, when I use delete on keyboard to clean all string to empty in TextInput components, It always show the first error picture, and when I DISMISS the error and reinput string, it show the second error picture, anyone know what happened here and how to solve it?</p>
  
  <h1>The render snippet</h1>
  
  <pre><code>    &lt;View&gt;
        &lt;View&gt;
          &lt;Text&gt;NickName&lt;/Text&gt; 
        &lt;/View&gt;
        &lt;View&gt;
          &lt;TextInput
            placeholder="NickName"
            onChangeText={(text) =&gt; SubjectStore.setDisplayName(text)}
            value={SubjectStore.displayName}
          /&gt;
        &lt;/View&gt;
      &lt;/View&gt;
  </code></pre>
  
  <h1>The store</h1>
  
  <pre><code>class SubjectStore {
    @observable user;
    @observable inSignupProcess;
  
    constructor(firebase) {
      this.user = null
    }
  
    @computed get displayName(){
      return this.user.displayName
    }
  
   @action setDisplayName(val){
     this.user.displayName = val
   }
  
  }
  </code></pre>
  
  <h1>First error picture</h1>
  
  <p><a href="https://i.stack.imgur.com/RePRb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RePRb.png" alt="enter image description here"></a></p>
  
  <h1>Second error picture</h1>
  
  <p><a href="https://i.stack.imgur.com/SYIJY.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/SYIJY.png" alt="enter image description here"></a></p>