How to make a NSDictionary String value like a [NSNull null]
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So I am creating a NSDictionary that is going to be passed across to another class as a paramater and then used in that class however it needs to be used.

There is one issue however, The NSDictionary has 18 values.. in this particular case only 3 are possibly used which I have got working fine, Although if in the case one of the three values is not used I would like to know how to make it look like the other entried I have in the NSdictionary [NSNull null]... Below is the code I am referring too.. I am just not sure what to do in this instance as I am fairly new to NSDictionary.. (have not used them very often).


// dont pay attention to the key id's as I have modified them for security purposed.


    // Keys for sendSeriesDictionary
        NSArray *keys = [NSArray arrayWithObjects:@"Code", @"MID", @"MD", @"SID",@"SMID",@"Yt",@"KID",@"KBID",@"K",@"CID",@"C",@"LT",@"Kep",@"KG",@"CD",@"LID",@"IHG",@"LID", nil];
        
        
        // Objects for keys that are for sendSeriesDictionary
        NSArray *objects = [NSArray arrayWithObjects: [NSNull null], MIDString, MDString, SIDString, [NSNull null], [NSNull null], [NSNull null], [NSNull null], [NSNull null], [NSNull null], [NSNull null], [NSNull null], [NSNull null], [NSNull null], [NSNull null], [NSNull null], [NSNull null], [NSNull null], nil];
        
        // Add keys and objects to NSDictionary
        NSDictionary *sendSeriesDictionary = [NSDictionary dictionaryWithObjects:objects forKeys:keys];

so for instance say if SIDString was empty, how could I replace that with or fill it with a value so it would act like the other [NSNull null] values... 

any help would be greatly appreciated.