title: Getting PFUser error when accessing username property when getting user as pointer
body: <p>Getting this error:</p>
  <pre><code>'NSInternalInconsistencyException', reason: 'Key &quot;username&quot; has no data.  Call fetchIfNeeded before getting its value.'
  </code></pre>
  <p>I have a joint class which contains <code>PFUser</code> as pointer. When I get a user from the joint class it just have pointer as expected but this condition fails and leads to error above:</p>
  <pre><code>if (user.username != nil) {
     username = user.username ?? &quot;no username&quot;
  } 
  
  /** THE ACCESSING property 
   The username for the `PFUser`.
   */
  @property (nullable, nonatomic, strong) NSString *username;
  </code></pre>