title: Nil string with [NSString stringWithFormat:] appears as "(null)"
body: <p>I have a 'Contact' class with two properties : firstName and lastName.
  When I want to display a contact's full name, here is what I do:</p>
  
  <pre><code>NSString *fullName = [NSString stringWithFormat:@"%@ %@", contact.firstName, contact.lastName];
  </code></pre>
  
  <p>But when the firstName and/or lastName is set to nil, I get a "(null)" in the fullName string. To prevent it, here's what I do:</p>
  
  <pre><code>NSString *first = contact.firstName;
  if(first == nil)  first = @"";
  NSString *last = contact.lastName;
  if(last == nil)  last = @"";
  NSString *fullName = [NSString stringWithFormat:@"%@ %@", first, last];
  </code></pre>
  
  <p>Does someone know a better/more concise way to do this?</p>