unexpected results from geocodeAddressString

Question

My question is, why are poiCoordinate's latitude and longitude properties coming out 0, 0 when addressTF.text has a very sensible address string, for example "1 Infinite Loop, Cupertino, CA 95014"?

//HomeViewController.m

@implementation HomeViewController

CLLocationCoordinate2D poiCoordinate;

-(void)performStringGeocode
{
    CLGeocoder *geocoder = [[CLGeocoder alloc] init];
    [geocoder geocodeAddressString:_addressTF.text completionHandler:^(NSArray *placemarks, NSError *error)
    {
        if (error)
        {
            NSLog(@"Geocode failed with error: %@", error);
            return;
        }
    CLPlacemark *placemark = [placemarks firstObject]; //Line A
    poiCoordinate = placemark.location.coordinate;     //Line B
    }];
}