title: KeychainItemWrapper returning NSZeroData?
body: <p>I am storing passwords on keychain using Apple's <code>KeychainItemWrapper</code>. At some point, if I try to fetch a password that was not setup yet using  </p>
  
  <pre><code>  KeychainItemWrapper* keychain = [[KeychainItemWrapper alloc] initWithIdentifier:identifier accessGroup:nil];
    NSString *password = [keychain objectForKey:kSecValueData];
  </code></pre>
  
  <p>password returns with this identification on the debugger</p>
  
  <pre><code>password = (_NSZeroData *) class name = _NSZeroData
  </code></pre>
  
  <p>If I let the code go on and try to use this value it will crash. </p>
  
  <p>This value is not a nil. If I test using <code>if (!password)</code> it will fail... and is not a string empty value (it will crash if I try to test it as a NSString).</p>
  
  <p>How do I test this thing to see if it is valid before proceeding?</p>