- iOS 2.0+
- macOS 10.2+
- tvOS 9.0+
- watchOS 2.0+
The CFNull opaque type defines a unique object used to represent null values in collection objects (which don’t allow
NULL values). CFNull objects are neither created nor destroyed. Instead, a single CFNull constant object—
k—is defined and is used wherever a null value is needed.
The CFNull opaque type is available in macOS 10.2 and later.