A DESCRIPTION OF THE PROBLEM :
If I try to transform from a StreamSource of an XML file having a comment between XML declaration and xml root element to a StaxResult (constructed from a XMLStreamWriter) I run into a
javax.xml.transform.TransformerException: org.xml.sax.SAXException: Can not output XML declaration, after other output has already been done.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
See java code

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The transformation does not throw an exception
ACTUAL -
The transformation throws a javax.xml.transform.TransformerException

---------- BEGIN SOURCE ----------
package org.apache.jackrabbit.vault.fs.io;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.Reader;
import java.io.StringReader;

import javax.xml.stream.XMLOutputFactory;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamWriter;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.stax.StAXResult;
import javax.xml.transform.stream.StreamSource;

public class Main {

    public static void main(String[] args) throws IOException, XMLStreamException, TransformerException {
        String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
                "<!--comment-->\n" +
                "<root />\n";
        try (Reader reader = new StringReader(xml);
             OutputStream out = new ByteArrayOutputStream()) {
                 XMLOutputFactory factory = XMLOutputFactory.newFactory();
                 XMLStreamWriter writer = factory.createXMLStreamWriter(out);
                 TransformerFactory tf = TransformerFactory.newInstance();
                 Transformer t = tf.newTransformer();
                 StreamSource source = new StreamSource(reader);
                 StAXResult result = new StAXResult(writer);
                 t.transform(source, result);
             }
    }
}
---------- END SOURCE ----------

FREQUENCY : always