title: Inserting nil objects into an NSDictionary
body: <p>If we have an API that requires only 2 out of an objects 5 properties and iPhone app doesn't require them to instantiate an object, when the object is used in the params NSDicitionary the app will crash. I was told NSDictionary will not let you assign nil values, as when it reaches nil it thinks its finished. Does objective-c have a way to spit out an objects non-nil properties into an NSDictionary?</p>
  
  <p>Example:</p>
  
  <pre><code>[Drunk alloc] init];
  drunk.started_drinking = [NSDate date];
  drunk.stopped_drinking (we don't set this because he is still a drunk)
  drunk.fat = YES;
  drunk.dumb = YES;
  
  
  parameters:@{
  
               @"auth_token" :token,
               @"name" : drunk.name, @"date_started" : drunk.started_drinking,
               @"date_stopped" : drunk.stopped_drinking, 
               @"prescribing_doctor" : drunk.fat,
               @"pharmacy" : drunk.dumb
  
              }
  </code></pre>
  
  <p>This will crash when it gets to the stopped_drinking property.  Any suggestions on how to handle this?</p>