root element no set error in jdom transformator

I'm getting the error:

[Fatal Error] :-1:-1: Premature end of file.
Exception in thread "main" java.lang.IllegalStateException: Root element not set
at org.jdom.Document.getContent(Document.java:307)
at org.jdom.output.XMLOutputter.output(XMLOutputter.java:679)

when trying to transform a jdom doc, based on XML file (A) with xslt (B), and output the transfomed file as html (C).

This is the code of the transformer:

package...
imports...
StreamSource xsltstreamsource = new StreamSource("./" + packagePath + "B.xslt");
Transformer transformer = TransformerFactory.newInstance().newTransformer(xsltstreamsource);
JDOMResult out = new JDOMResult();
transformer.transform(new JDOMSource(jdoc), out);
XMLOutputter xmloutputter = new XMLOutputter(" ",true);
xmloutputter.setTextNormalize(true);
xmloutputter.output(out.getDocument(), new FileWriter("./" + packagePath + "C.html"));

Now, jdoc is the jdom doc that was created from:
File xmlfile = new File("./" + packagePath + "A.xml");
SAXBuilder builder = new SAXBuilder();
jdoc = builder.build(xmlfile);

What am i doing wrong? i'm sure that the xml and the xslt are valid, and i did not get errors when the jdoc was built.