XalanTransform warning: Invalid argument in nodeset()

I am unable to get rid of warning "Invalid argument type in the function
'nodeset()'" given by XalanTransform.

The code is as follows:
<xsl:variable name="datatypes" select="/xip/datatypes"/>
...
<xsl:with-param name="filters" select="xalan:nodeset($filters)"/>
...

If I define the variable in the file instead of assigning from input
file, the warning goes off.

<xsl:variable name="datatypes">
<abc>
        <bcd>
        </bcd>
</abc>
...
<xsl:with-param name="filters" select="xalan:nodeset($datatypes)"/>
...

Any clues?
Prashant


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