title: iOS13 DiffableDataSource Invalid parameter not satisfying: indexPath || ignoreInvalidItems
body: <p>I'm converting my collection view to new iOS13 UICollectionViewDiffableDataSource... so I need to update cell information on demand.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>let snap = self.diffDataSouce.snapshot
  snap?.reloadItems(withIdentifiers: [itemToUpdate]) //reload cell info
  self.diffDataSouce.apply(snap, animatingDifferences: true)
  </code></pre>
  
  <p>But I get <code>Invalid parameter not satisfying: indexPath || ignoreInvalidItems</code> ...why?
  My current <code>snap</code> contains <code>itemToUpdate</code> and also my array of models...</p>
  
  <p>I think it's because <code>snap.indexOfItemIdentifier(itemToUpdate)</code> returns not found (NSNotFound)...but that's should be impossible according data model.</p>
  
  <p>Have you some hints?</p>