title: __NSCFString objectForKeyedSubscript: exception
body: <p>I take datas from server. My app work fine in Sinulator and test device iPhone 4s, but one man have problem on iPod 4. He get exception:</p>
  
  <pre><code>-[__NSCFString objectForKeyedSubscript:]: unrecognized selector sent to instance 0x1d263a20
  </code></pre>
  
  <p>I cann't use this device so I write code to know where crash was.</p>
  
  <pre><code> if (![dictionaryRest[@"compliments"] isEqual:[NSNull null]]) {
         NSMutableArray *array = [NSMutableArray new];
         NSMutableArray *firstArray = [NSMutableArray new];
         for (NSDictionary *dic in dictionaryRest[@"compliments"]) {
              Compliment *compl = [Compliment new];
              if (![dic[@"ID_promotions"] isEqual:[NSNull null]])
                  compl.ID = [dic[@"ID_promotions"] integerValue];
  </code></pre>
  
  <p>So in last 2 strings this exception was. What the reason of this? So I understand that I need use</p>
  
  <pre><code>if ([dict objectForKey:[@"compliments"])
  </code></pre>
  
  <p>instead</p>
  
  <pre><code>if (![dict[@"compliments"] isEqual:[NSNull null]])
  </code></pre>
  
  <p>and in all another cases.</p>
  
  <p>I test now and I have in my dictionary for ID:
  <img src="https://i.stack.imgur.com/tQkzN.png" alt="enter image description here"></p>