[xsl] Deciding whether param contains nodeset

Hi,

i have an template

	<xsl:template name="test">
		<xsl:param name="repl" select="''"/>
	</xsl:template>

Sometimes i call this template with repl = string, sometimes i want to
call it with repl = nodeset.

When i apply-templates on repl and repl is a string, so the following
execption arises:
org.apache.xpath.XPathException: #RTREEFRAG kann nicht in NodeList
konvertiert werden!
							  (in english:
cannot be converted in nodeset)

So i wonder whether it is possible to decide if repl is a string or a
nodeset.
If repl = string output should be the value of the String
if repl = nodeset output should be apply-templates nodeset

How can i decide in "test" which type the param repl is of?

Regards,
Thomas.