XMLUnit throws NullPointerException when creating Diff object for valid xml

Question

I am using org.custommonkey.xmlunit; (version 1.2). While building Diff object: Diff diff = new Diff(expected, generated);

I always have NullPointerException as it's failing on this.controlDoc = this.getManipulatedDocument(controlDoc);. While debugging I found that in first constructor:

public Diff(String control, String test) throws SAXException, IOException {
        this((Reader)(new StringReader(control)), (Reader)(new StringReader(test)));
    }

there are proper xmls however when:

public Diff(Reader control, Reader test) throws SAXException, IOException {
        this(XMLUnit.buildDocument(XMLUnit.newControlParser(), control), XMLUnit.buildDocument(XMLUnit.newTestParser(), test));
    }

is called I see in debugger [#document: null]. Why is that so? I tried with many xmls, even really easy and small which I found in internet but nothing works.

Answer 1

Oh, I just have found that XMLUnit.setIgnoreWhitespace(true); cause this problem because in project I am using Saxon library in ancient version and it was fixed in version 8.9 however this:

XMLUnit.setTransformerFactory("org.apache.xalan.processor.TransformerFactoryImpl");

helps a lot.