关于Apache FOP的转换程序不能通过，请高手看看。

[squirrel_1976]

import java.io.*;
import javax.xml.transform.*;
import javax.xml.transform.sax.*;
import javax.xml.parsers.*;
import javax.xml.transform.stream.StreamSource;
import org.apache.fop.apps.*;
import org.xml.sax.*;

public class XML2PDF {
public static File xml = new File("D:\\ATML_Q1_2000.xml");
public static File xslt = new File("D:\\XBRL.xslt");

public XML2PDF() {
}

public static void main(String[] args) {
try {
Driver driver = new Driver();
XSLTInputHandler input = new XSLTInputHandler(xml, xslt);

FileOutputStream os = new FileOutputStream("D:\\sample.pdf");
driver.setOutputStream(os);
driver.setRenderer(Driver.RENDER_PDF);

driver.render(input.getParser(), input.getInputSource());
}catch (Exception e) {
e.printStackTrace();
}
}
}

程序如上，这是一个教程式的程序啦。但我运行（fop 0.20.4）时报错：
[ERROR] Unknown formatting object ^html
java.lang.RuntimeException: java.lang.NullPointerException
at org.apache.xalan.transformer.TransformerImpl.run(TransformerImpl.java:3170)
at org.apache.xalan.transformer.TransformerHandlerImpl.endDocument(TransformerHandlerImpl.java:433)
at org.apache.xerces.parsers.AbstractSAXParser.endDocument(Unknown Source)
at org.apache.xerces.impl.XMLDocumentScannerImpl.endEntity(Unknown Source)
at org.apache.xerces.impl.XMLEntityManager.endEntity(Unknown Source)
at org.apache.xerces.impl.XMLEntityManager$EntityScanner.load(Unknown Source)
at org.apache.xerces.impl.XMLEntityManager$EntityScanner.skipSpaces(Unknown Source)
at org.apache.xerces.impl.XMLDocumentScannerImpl$TrailingMiscDispatcher.dispatch(Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
at org.apache.xerces.parsers.DTDConfiguration.parse(Unknown Source)
at org.apache.xerces.parsers.DTDConfiguration.parse(Unknown Source)
at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
at org.apache.xalan.transformer.TrAXFilter.parse(TrAXFilter.java:134)
at org.apache.fop.apps.Driver.render(Driver.java:457)
at com.megasoft.xbrl.demo.consumer.XML2PDF.main(XML2PDF.java:45)

请问是何缘故？而换用0.20.5版本后又错的不一样。