[] Objective-C: How to Load TIFF, Burn-in Annotations, and Save with No UI - Cannot create Context

-(int)weekendAtBurnies
{
    int rc = 0;
    NSError *error;
    
    // work from user/Downloads
    NSFileManager *fm = [NSFileManager defaultManager];
    NSURL *downloadsURL = [fm URLForDirectory:NSDownloadsDirectory
                                     inDomain:NSUserDomainMask
                            appropriateForURL:nil
                                       create:YES
                                        error:&error];
    NSURL *furl = [NSURL URLWithString:@"ocr1.tif" relativeToURL:downloadsURL]; // source image
    NSURL *aurl = [NSURL URLWithString:@"A_0.tif" relativeToURL:downloadsURL];  // saved image
    NSURL *xurl = [NSURL URLWithString:@"redact.ann.xml" relativeToURL:downloadsURL];   // anno xml
    
    // create annotation container from xml
    LTAnnCodecs *annCodecs = [[LTAnnCodecs alloc] init];
    NSString *xmlData = [NSString stringWithContentsOfURL:xurl usedEncoding:nil error:&error];
    NSLog(@"%@", xmlData);
    LTAnnContainer * container = [annCodecs loadXmlData:xmlData pageNumber:1];
    // list them
    for (int i = 0; i < container.children.count; i++)
    {
        LTAnnObject *annObj = container.children[i];
        NSLog(@"%@\n", [annObj friendlyName]);
    }
    
    LTRasterCodecs *codecs =[[LTRasterCodecs alloc] init];
    LTRasterImage *sourceImage = [codecs loadURL:furl error:&error];
    BOOL setResolution          = NO;
    int imageDpiX               = 0;
    int imageDpiY               = 0;
    
    if (sourceImage.xResolution != 72 || sourceImage.yResolution != 72)
    {
        setResolution = YES;
        imageDpiX     = (uint)sourceImage.xResolution;
        imageDpiY     = (uint)sourceImage.yResolution;
    }

    
    LTAnnContainerMapper *mapper = [container.mapper copy];
    container.mapper = [[LTAnnContainerMapper alloc] initWithSourceDpiX:sourceImage.xResolution
                                                             sourceDpiY:sourceImage.yResolution
                                                             targetDpiX:sourceImage.xResolution
                                                             targetDpiY:sourceImage.yResolution];
    [sourceImage.linkedImage lockFocus];
    
    CGImageRef imgRef = [LTRasterImageConverter convertToCGImage:sourceImage
                                                         options:LTConvertToImageOptionsNone
                                                           error:&error];
    NSBitmapImageRep *refrep = [[NSBitmapImageRep alloc] initWithCGImage:imgRef];

    //
    // this always returns nil. WHY! WHY! WHY!
    NSGraphicsContext *context = [NSGraphicsContext graphicsContextWithBitmapImageRep:refrep];
    //
    
    [NSGraphicsContext saveGraphicsState];
    CGContextRef contextRef = [context CGContext];
    CGContextTranslateCTM(contextRef, 0, sourceImage.height);
    CGContextScaleCTM(contextRef, 1, -1);
    
    // render annotations onto source image
    LTAnnUniversalRenderingEngine *renderingEngine = [[LTAnnUniversalRenderingEngine alloc] init];
    [renderingEngine attachContainer:container context:contextRef];
    //We will use the burnScaleFactor property to burn the objects with fixed states correctly
    LeadRectD testRect =   [container.mapper rectFromContainerCoordinates:LeadRectDMake(0, 0, 10, 10) operations:(LTAnnFixedStateOperationsNone)];
    LeadRectD scaledRect =  [mapper rectFromContainerCoordinates:LeadRectDMake(0, 0, 10, 10) operations:(LTAnnFixedStateOperationsNone)];
    double scaleFactor = scaledRect.width / testRect.width;
    container.mapper.burnScaleFactor /= scaleFactor;
    
    [renderingEngine burn];
    [NSGraphicsContext restoreGraphicsState];
    [sourceImage.linkedImage unlockFocus];
    
    [renderingEngine detach];
    
    // save rendered image into dest.
    LTCodecsImageInfo *info = [codecs imageInformationForURL:furl totalPages:YES error:&error];
    [codecs save:sourceImage url:aurl format:LTRasterImageFormatTif bitsPerPixel:info.bitsPerPixel error:&error];
    
    return rc;
}