App crash after ' - objective-c

Question

My application is crashing when a ' appears in the title of the JSON code i'm parsing.
This line is loading the title's:
[[cell textLabel] setText:[item objectForKey:#"title"]];
JSON:
NSString *jsonString = [NSString
stringWithContentsOfURL:[NSURL URLWithString:#"**test.php"]
encoding:NSStringEncodingConversionAllowLossy
error:nil];
// Create parser
SBJSON *parser = [[SBJSON alloc] init];
NSDictionary *results = [parser objectWithString:jsonString error:nil];
parser = nil;
// Set tableData
[self setTableData:[results objectForKey:#"items"]];
Crash:
tableData NSArray * 0x00000001
2012-04-10 10:29:11.446 *[21222:f803] -[NSNull isEqualToString:]:
unrecognized selector sent to instance 0x146ace8 2012-04-10
10:29:11.447 *[21222:f803] * Terminating app due to uncaught
exception 'NSInvalidArgumentException', reason: '-[NSNull
isEqualToString:]: unrecognized selector sent to instance 0x146ace8'
* First throw call stack: (0x13d4022 0x1565cd6 0x13d5cbd 0x133aed0 0x133acb2 0x15e0ff 0x2b10 0xb8c54 0xb93ce 0xa4cbd 0xb36f1 0x5cd21
0x13d5e42 0x1d8c679 0x1d96579 0x1d1b4f7 0x1d1d3f6 0x1db81ce 0x1db8003
0x13a8936 0x13a83d7 0x130b790 0x130ad84 0x130ac9b 0x12bd7d8 0x12bd88a
0x1e626 0x1ded 0x1d55) terminate called throwing an exception(lldb)

Answer 1

The key part of that crash info is: unrecognized selector sent to instance ... [NSNull isEqualToString:]
It looks like your JSON contains null somewhere that you are expecting a string. Later on, probably inside of setTableData: you will be doing something like this:
NSString* whatever = [items objectForKey:#"whatever"];
if([whatever isEqualToString:#"hello"]){
...
}
And that will crash, because the whatever variable contains NSNull, not an NSString like you were expecting.