Swift and __nullable and _nonnull

exampleWarning.swift

class Pet {

  func assignOwnerForCat(cat: Cat!, withSerial serial: Int!)

}

...

func serialAssignmentForCat(cat: Cat, forSerial serial: Int?) {

  var snuggles = Pet()

  snuggles.assignOwnerForCat(cat, withSerial: serial) 

  

}

...
class PFObject {

    func setObject(object: AnyObject, forKey key: String)

}

func createObjectWithName(name: String, forKey key: String?) {

  let object = PFObject(className: "Object")

  object.setObject(name, forKey: key)

}

Pet.m

@interface Pet: NSObject{
  -(void)assignOwnerForCat(NON_NULL id)cat withSerial:(NON_NULL NSNumber*)serial;
}
@end
@implementation Pet{

- (void)serialAssignmentForCat:(Cat *)cat forSerial:(nullable NSNumber *)erial
  ...
  [pet assignOwnerForCat:cat forSerial:serial];
}
}