title: NSJSONSerialization results in EXC_BAD_ACCESS
body: <p>Currently I am writing an app (Target iOS 6, ARC enabled) that uses JSON for data transmission and Core Data for persistent storage. The JSON data is generated out of a MySQL database by a PHP script via json_encode.</p>
  
  <p>My Problem is that with data from certain tables the following code fails:</p>
  
  <pre><code>- (NSDictionary *)executeFetch:(NSString *)query
  {
      NSURL *requesturl = [NSURL URLWithString:[query stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
  
      NSError *dataError = nil;
      self.jsonData = [NSData dataWithContentsOfURL:requesturl options:kNilOptions error:&amp;dataError];
  
      NSError *error = nil;
      self.jsonSerializationResult = [NSJSONSerialization JSONObjectWithData:self.jsonData options:NSJSONReadingMutableContainers|NSJSONReadingMutableLeaves error:&amp;error];
  
      return self.jsonSerializationResult;
  
  }
  </code></pre>
  
  <p>The program always crashes with an EXC_BAD_ACCESS error on the line where it says self.jsonSerializationResult and Instruments says that there was a Zombie detected. I know that this means that some object I send a message to is nil, but I can't find out how to fix it... That's what Instruments has to say: </p>
  
  <pre><code>#   Address Category    Event Type  RefCt   Timestamp   Size    Responsible Library Responsible Caller
  0   0xa1b8a70   CFString (mutable)  Malloc  1   00:01.603.081   32  Foundation  -[NSPlaceholderMutableString initWithBytesNoCopy:length:encoding:freeWhenDone:]
  1   0xa1b8a70   CFString (mutable)  Release 0   00:01.603.137   0   Foundation  newJSONValue
  2   0xa1b8a70   CFString (mutable)  Zombie  -1  00:01.603.259   0   Foundation  newJSONString
  </code></pre>
  
  <p>My program works with every JSON output except for this one:</p>
  
  <pre><code>{
     "termin":[
        {
           "termin_id":"17",
           "veranstaltung_id":"20",
           "beginn":"2012-09-28 17:00:00",
           "ende":"2012-09-28 18:00:00",
           "freie_pl\u00e4tze":null
        },
        {
           "termin_id":"18",
           "veranstaltung_id":"26",
           "beginn":"2012-09-28 19:00:00",
           "ende":"2012-09-28 20:00:00",
           "freie_pl\u00e4tze":null
        },
        {
           "termin_id":"19",
           "veranstaltung_id":"26",
           "beginn":"2012-09-28 21:00:00",
           "ende":"2012-09-28 22:00:00",
           "freie_pl\u00e4tze":null
        },
        {
           "termin_id":"20",
           "veranstaltung_id":"46",
           "beginn":"2012-09-28 19:00:00",
           "ende":"2012-09-28 20:00:00",
           "freie_pl\u00e4tze":null
        },
        {
           "termin_id":"24",
           "veranstaltung_id":"66",
           "beginn":"2012-09-28 22:00:00",
           "ende":"2012-09-28 22:30:00",
           "freie_pl\u00e4tze":"120"
        }
     ]
  }
  </code></pre>
  
  <p>I thought about some possible error sourced but none seems to be the responsible:</p>
  
  <ul>
  <li>jsonData or jsonSerializationResult could be nil: they aren't</li>
  <li>PHP generated invalid JSON: checked for that with a validator</li>
  <li>null Values: not a problem with other tables</li>
  </ul>
  
  <p>Has anybody got an idea?</p>