[xsl] An XPath expression that avoids writing special case code?

Hi Folks,

My XML document contains a bunch of <Row> elements, like so:

<Document>
    ...
    <Row>
        <Cell>
            <Data>airport</Data>
        </Cell>
        <Cell>
            <Data>airports</Data>
        </Cell>
    </Row>
    ...
</Document>

I want to fetch the Row whose Cell[1]/Data is 'airport' and whose Cell[2]/Data 
is 'airports'. So I created this XPath expression:

/Document/Row[Cell[1]/Data eq 'airport'][Cell[2]/Data eq 'airports']

I do this kind of fetching operation often, so I created a function to fetch 
the desired Row:

<xsl:function name="f:getRow">
    <xsl:param name="element"/>
    <xsl:param name="parent"/>
    <xsl:sequence select="$document/Row[Cell[1]/Data eq $element][Cell[2]/Data 
eq $parent]" />
</xsl:function>

I call the function this way:

<xsl:sequence select="f:getRow('airport', 'airports')" />

Sometimes there is an element that doesn't have a parent. That is, sometimes 
I'd like to fetch a Row in which Cell[2] is empty, like this:

    <Row>
        <Cell>
            <Data>aviation</Data>
        </Cell>
        <Cell/>
    </Row>

Then this call to f:getRow fails:

<xsl:sequence select="f:getRow('aviation', '')" />        <!-- Those are two 
apostrophes within the parentheses -->

Clearly I need to modify f:getRow. I could add special case code to test 
$parent to see if it is empty (the '' string) and do one thing, and if it's not 
empty do another thing. But I wonder if there is a more elegant solution that 
doesn't involve special case code? Is there a way to modify the XPath 
expression in f:getRow such that it fetches the correct Row regardless of 
whether $parent is empty or not?

/Roger
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