I use 0.20.1 also with SAX events. I had to add this to get rid of the null pointer:
//Hack fix for FOP bug. Might be unnecessary in FOP 0.20.3.
StreamRenderer x = new StreamRenderer(outputStream,
pdfDriver.getRenderer());
((FOTreeBuilder)pdfDriver.getContentHandler
()).setStreamRenderer(x);
Hope this helps,
-Ryan
