title: Swift - Error: unexpectedly found nil while unwrapping an optional value
body: <p>I have been making an app in Swift but I keep getting an error in my TableViewController class. I could not find any way to fix this and kept getting this error : </p>
  
  <pre><code>override func tableView(tableView: UITableView?, cellForRowAtIndexPath indexPath: NSIndexPath!) -&gt; UITableViewCell!  {
          let cell : TextTableViewCell = tableView!.dequeueReusableCellWithIdentifier("Cell", forIndexPath : indexPath!) as TextTableViewCell
  
      let madan : PFObject = self.timeLineData.objectAtIndex(indexPath!.row) as PFObject
  
      cell.timestampLabel.alpha = 0
      cell.usernameLabel.alpha = 0
      cell.madanTextView.alpha = 0
  
      cell.madanTextView.text = madan.objectForKey("content") as String
  
      var dateFormatter : NSDateFormatter = NSDateFormatter()
      dateFormatter.dateFormat = "MM-dd-yyyy HH:mm"
      cell.timestampLabel.text = dateFormatter.stringFromDate(madan.createdAt)
  
      var findSender : PFQuery = PFUser.query()
      findSender.whereKey("objectId", equalTo: madan.objectForKey("sender").objectId)
      var i = 1
      findSender.findObjectsInBackgroundWithBlock {
          (objects: [AnyObject]!, error: NSError!) -&gt; Void in
          if !error {
              let user : PFUser = (objects as NSArray).lastObject as PFUser // Error here
  
              cell.usernameLabel.text = user.username 
  
              UIView.animateWithDuration(0.5, animations: {
  
                  cell.timestampLabel.alpha = 1
                  cell.usernameLabel.alpha = 1
                  cell.madanTextView.alpha = 1
  
              })
          }
      }    
      return cell
  }
  </code></pre>
  
  <p>I cannot find any way to fix this.</p>