title: [NSNull length]: unrecognized selector sent to instance in objective-c
body: <p>I am getting some JSON data from a service, one property is a string to represent an image url, it seems what is returned is NULL, I do the check but XCode breaks before my if statement and generate an exception. this is my code below:</p>
  
  <pre><code>- (void)configureCellForAlbum:(Album *)album {
  
      self.albumTitle.text = album.albumTitle;
      self.artisteName.text = album.artisteName;
      NSURL *imageUrl = [NSURL URLWithString:album.thumbnail];
      if (imageUrl == nil) {
          self.albumThumbnail.image = [UIImage imageNamed:@"music_record"];
      }
      else {
          self.albumThumbnail.imageURL = imageUrl;
      }
  }
  </code></pre>
  
  <p>the exception is </p>
  
  <blockquote>
    <p>Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull length]: unrecognized selector sent to instance.</p>
  </blockquote>
  
  <p>How do I do the check so that if the value retured is null, it uses a local image but if not null to use the image string url that is returned?</p>