A convenience thing, just some null types for common structs and a way to check for them. Idea from this SO: http://stackoverflow.com/questions/11987142/sending-nil-to-cgpoint-type-parameter

ABNullStructs.h

const CGPoint ABCGPointNull  =  {(CGFloat)NAN, (CGFloat)NAN};
const UIOffset ABUIOffsetNull =  {(CGFloat)NAN, (CGFloat)NAN};
const CGSize ABCGSizeNull   =  {(CGFloat)NAN, (CGFloat)NAN};

BOOL ABCGPointIsNull( CGPoint point ){
    return isnan(point.x) && isnan(point.y);
}
BOOL ABUIOffsetIsNull( UIOffset offset ){
    return isnan(offset.horizontal) && isnan(offset.vertical);
}
BOOL ABCGSizeIsNull( CGSize size ){
    return isnan(size.width) && isnan(size.height);
}