title: Check key exists in NSDictionary
body: <p>how can I check if this exists?:</p>
  
  <pre><code>[[dataArray objectAtIndex:indexPathSet.row] valueForKey:@"SetEntries"]
  </code></pre>
  
  <p>I want to know whether this key exists or not. How can I do that?</p>
  
  <p>Thank you very much :)</p>
  
  <p><strong>EDIT:
  dataArray has Objects in it. And these objects are NSDictionaries.</strong></p>