title: How to check if is null in react native?
body: <p>I'm trying to validate data from firebase.</p>
  <p>try {</p>
  <pre><code> const id = this.context.getCurrentUser( { } ).uid  //get user's id
  
   const user = await this.context.validPlantao(id) // check if got data from firebase. 
  </code></pre>
  <p>above 'const user' it' s working, If got some data, return these infos, but if is empty returns null.</p>
  <p>i've gotta verify this code below</p>
  <pre><code>            if(user == null){
                  console.log('can register data') 
                                  
              }else{
                  console.log('you even are registered') 
              }
  </code></pre>
  <p>That If condition isn't working.
  When have nothing in firebase 'const user' returns null. What i want to do is check, if have no register, they can save. But, if have an register, show an alert mensager</p>