Creating an Empty Array

To create an empty array use NSNull:

NSNull *myNull = [NSNull null];
NSMutableArray *arr = [NSMutableArray arrayWithObjects: myNull, myNull, nil];


Then to compare use something like:

if ([arr objectAtIndex:index]  == (id)[NSNull null]) {

  //do something
}


nil cannot be added into an Array or collection similar to how an int cannot be added.  NSNull is the helper object to get nil into the collection.  In Objective C there's nil, NSNull and Null.

NSNull, nil, null differences

Found a great answer on stack overflow.  Here's the gist of it:

nil is like (NSObject *)0
NULL is like (void*)0
Both are pointers with an integer value of zero.

NSNull is a helper object to add nil to NSArray or container classes requiring an object.  Similar to how NSNumber is needed to add an int.  [NSNull null] can be used instead of nil.  You can't compare NSNull to nil, but you can check if something is a NSNull.