Exclude processing instruction from XSLT

I have a simple plain-text-generating XSLT that I am applying like this (using the reference implementation):

    StreamSource schemasource = new StreamSource(getClass().getResourceAsStream("source.xml"));
    StreamSource stylesource = new StreamSource(getClass().getResourceAsStream("transform.xslt"));
    Transformer transformer = TransformerFactory.newInstance().newTransformer(stylesource);

    StringWriter writer = new StringWriter();
    transformer.transform(schemasource, new StreamResult(domWriter));
    System.out.println("XML after transform:");
    System.out.println(writer.toString());

The "transform" call always inserts an processing instruction in the output. Is there any way to configure it not to do so?

(For example for a very simple node identity transform

<xsl:stylesheet version="1.0" xmlns:xsl="http://ift.tt/tCZ8VR" xmlns:xs="http://ift.tt/tphNwY">
    <xsl:template match="*">
        <xsl:copy/>
        <xsl:apply-templates/>
    </xsl:template>
</xsl:stylesheet>

when applied to

<hello/>

I get

<?xml version="1.0" encoding="UTF-8"?>
<hello/>

)

Many thanks, Andy