Document doc = docBuilder.newDocument();
            Element rootElement = doc.createElement(EcoreUtility.getFeatureName(object));


            Element children = null;
            Text text = null;

            for(EAttribute attr : list) {

                children = doc.createElement(attr.getName());
                text = doc.createTextNode(EcoreUtility.getFeatureValue(object, attr.getName()));
                children.appendChild(text);
                rootElement.appendChild(children);
            }

            doc.appendChild(rootElement);

transformer.transform(new DOMSource(doc), new StreamResult(writer));

java.lang.NullPointerException
    at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.characters(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)

for(EAttribute attr : list) {
...
..
}