java - NULL ポインター例外を返すトランスフォームですが、パラメーターは NULL ではありませんか?

Question

KML ファイルを生成していますが、Transformer API を使用する時点で NullPointerException 例外が発生します。私も参照しているコードは次のとおりです。

TransformerFactory transformerFactory = TransformerFactory.newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(kml);
            StreamResult result = new StreamResult(new File("src/mapa/mapa.kml"));
            System.out.print("DESPRES DE CREAR RESULT\n");
            if(source == null)
                System.out.print("SOURCE IS NULL");
            if(result == null)
                System.out.print("RESULT IS NULL");
            transformer.transform(source, result);
            System.out.print("AFTER TRASNFORM\n");

NULL の System.out は出力されませんが、最後の System.out も出力されません。なぜNPEを与えているのですか?

例外：

DESPRES DE CREAR RESULT
ERROR:  ''
javax.xml.transform.TransformerException: java.lang.NullPointerException
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at Joc.crearMapa(Joc.java:199)
    at MastersOfWar.main(MastersOfWar.java:18)
Caused by: 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)
    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.TransformerImpl.transformIdentity(Unknown Source)
    ... 4 more
---------
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)
    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.TransformerImpl.transformIdentity(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at Joc.crearMapa(Joc.java:199)
    at MastersOfWar.main(MastersOfWar.java:18)