[xsl] Function to accept node and name of subnode in parameter string

["Bordeman, Chris" <Chris.Bordeman@xxxxxxxxxxxxxxxxx>]

Hi all.  I need to create a 2.0 function that will accept an element()?
and a xs:string.  The string will contain the name of a subnode of the
first parameter.

The function will do something like this:

<!-- Given any node and the name of a subnode, returns
     the nonempty subnode's value or N/A -->
<xsl:function name="fn:ValueOrNA" as="xs:string">
	<xsl:param name="node" as="element()?"/>
	<xsl:param name="childelementname" as="xs:string"/>
	<xsl:choose>
		<xsl:when test="$node and $node/$childname != ''">
			<xsl:value-of select="$node/$childname"/>
		</xsl:when>
		<xsl:otherwise>
			<xsl:value-of select="'N/A'"/>
		</xsl:otherwise>
	</xsl:choose>
</xsl:function>

But it always seems to return just the second string I pass in, not the
value of the subnode.

What's the right way to do this?

Thanks.