How can I check If I got null from json?

Question

Here I got from JSON

[{"photo":null}]

and I use this code

NSMutableArray *jPhoto = [NSMutableArray arrayWithArray:(NSArray *)[jsonDict valueForKey:@"photo"]];

How can I check it if I want to use if() ??

edit

here is JSON Data

   [{"photo":
              [{"image":"http:\/\/www.yohyeh.com\/upload\/shisetsu\/13157\/photo\/1304928459.jpg","title":"test picture","content":"this is description for test picture.\r\n\u8aac\u660e\u6587\u306a\u306e\u306b\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb"}
              ,{"image":"http:\/\/www.yohyeh.com\/upload\/shisetsu\/13157\/photo\/1304928115.jpg","title":"nothing","content":"iMirai"}
              ,{"image":"http:\/\/www.yohyeh.com\/upload\/shisetsu\/13157\/photo\/1303276769.jpg","title":"iMirai","content":"Staff"}]}
  ]

and here is my JSON parser

NSError *theError = nil;     
    NSString *URL = [NSString stringWithFormat:@"http://www.yohyeh.com/apps/get_sub_detail.php?id=%@&menu=photo",g_id];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:URL]];
    NSURLResponse *theResponse =[[[NSURLResponse alloc]init] autorelease];
    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&theResponse error:&theError];   
    NSMutableString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

    NSDictionary *jsonDict = [string JSONValue];

Thank for help