title: unexpectedly found nil while unwrapping an Optional value?
body: <p>I'm facing with an error: <strong>"unexpectedly found nil while unwrapping an Optional value"</strong> 
  when I insert new data in coreData and reload my tableview, I recall this function</p>
  
  <pre><code>  var unique = [String]()
    var loadMovie = [String:[Movie]]()
  
  
   func insertMovie(movie : Movie) {
      let genre = movie.genre!
      if unique.contains(genre) {
          loadMovie[genre]!.append(movie)
      } else {
          unique.append(genre)
          loadMovie[genre] = [movie]
      }
  }
  </code></pre>
  
  <p>and fetch data:</p>
  
  <pre><code> func fetchAndSetResults() {
      let app = UIApplication.sharedApplication().delegate as! AppDelegate
      let context = app.managedObjectContext
      let fetchRequest  = NSFetchRequest(entityName: "Movie")
  
      do {
          let movies = try context.executeFetchRequest(fetchRequest) as! [Movie]
          loadMovie.removeAll()
          for movie in movies {
          insertMovie(movie)
          }
      } catch let err as NSError {
          print(err.debugDescription)
      }
  }
  </code></pre>
  
  <p>and the app crushes for the error mentioned above on line: "            loadMovie[genre]!.append(movie)" but if I reload app, my data are stored and visible in tableview. What's the problem?</p>