title: dictionary Value of type 'Int?' has no member
body: <p>I use this code that find value for key in dictionary and remove value.</p>
  
  <pre><code>var downloadQ = [Int: Int]()
  
  downloadQ[id] = indexPath.row
  </code></pre>
  
  <p>but I get error in this line <code>if let idx = downloadQ[id].index(of: indexPath.row) {</code> error: <code>Value of type 'Int?' has no member 'index'</code></p>
  
  <pre><code>if let idx = downloadQ[id].index(of: indexPath.row) {
      self.downloadQ[id].remove(at: idx)
  }
  </code></pre>
  
  <p>How to fix it?</p>