drawing to BufferedBitmap with the new Graphics Pool API level 4.0

Hello, I can't figure out how to draw to the BufferedBitmap object created with the Graphics.createBufferedBitmap() method introduced with APi level 4.0

// PRE 4.0
var bb = new Graphics.BufferedBitmap({:width=>100, :height=>100});
var bbDc = bb.getDc();
bbDc.setColor(0xFFFFFF, 0x000000);
bbDc.clear();
bbDc.fillCircle(50, 50, 25);
dc.drawBitmap(120, 120, bb);

// NEW
var bbr = Graphics.createBufferedBitmap({:width=>100, :height=>100});
var bb = bbr.get();
var bbDc = bb.getDc(); // doesn't work !