Empty String param

I want to declare an xsl parameter which is a string, and may be empty
when called.
The system doesn't seem to allow me to do this.
I'm using Saxon-9.

I say

<xsl:template name="insert">
<xsl:param name="default" />
<!-- various stuff using $default-->
</xsl:template>

And eventually I do
<xsl:call-template name="insert">
<xsl:with-param name="default" select="$named-nodes[1]/@default" />
</xsl:call-template>

So that I can get the value of default from an atribute in another
document ($named-nodes).
This attribute may be, and often is, absent.  In which case I'd expect
default to be an empty string. Which it is for this test.


I get an error as follows :
XTTE0570: An empty sequence is not allowed as the value of parameter
$default.
Referring to the xsl:with-param line.

Why can't I pass in the empty string here ?
(ie why is it telling me that an empty sequence (should be a string) is
not allowed ?)

I have tried adding as="xs:string" to the xsl:with-param and also to the
xsl:param as I'd have thought that even though it may be the case that
the processor would reject an empty node-set or sequence if I was
passing one it should surely expect a string to be allowed to be empty.



Richard Kerry
Colledia Control Engineer
Siemens IT Solutions and Services Ltd
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