title: Cocoa/Objective-C - Verify if a key exist on a NSDictionary
body: <p>How do I verify if a key exists on a <code>NSDictionary</code>?</p>
  
  <p>I know how to verify if it has some content, but I want to very if it is there, because it's dynamic and I have to prevent it. Like in some cases it could happen to have a key with the "name" and is value, but in another cases it could happen that this pair of value don't exists.</p>