Facebook provides date objects in the format: `2010-12-01T21:35:43+0000`

I want to convert this format to NSDate.

I am using the following code. Why does it return `null`.

```
NSDateFormatter *df = [[NSDateFormatter alloc] init];
dateString = [dateString stringByReplacingOccurrencesOfString:@"T" withString:@" "];
dateString = [dateString stringByReplacingOccurrencesOfString:@"+" withString:@" +"];
NSLog(@"%@", dateString);
[df setDateFormat:@"yyyy-MM-dd HH:mm:ss '+'ZZZZ"];
NSLog(@"%@",df.dateFormat);
NSDate *date = [df dateFromString:dateString];

NSLog(@"%@ date",date);

```