how to check and replace the null date using xslt - xslt

Question

I want to check if my expiry date is null than i want to take the value from CreationDate.
My XML is like
<CreationDate>2017-03-18</CreationDate> <ExpiresDate>20170318</ExpiresDate>
and in my xsl
<xsl:element name="NewDeliveryDueDate">
<xsl:call-template name="FormatDate">
<xsl:with-param name="DateTime" select="Product/ExpiresDate"/>
</xsl:call-template>
</xsl:element>
&comma;
Please suggest.

Answer 1

Your question is incomplete. Perhaps this could work for you:
XSLT 1.0
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:strip-space elements="*"/>
<!-- identity transform -->
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="ExpiresDate[not(string())]">
<xsl:copy>
<xsl:value-of select="translate(../CreationDate, '-', '')"/>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
When this is applied to the following example input:
<root>
<item>
<CreationDate>2017-03-18</CreationDate>
<ExpiresDate>20170318</ExpiresDate>
</item>
<item>
<CreationDate>2017-03-09</CreationDate>
<ExpiresDate/>
</item>
</root>
the result will be:
<?xml version="1.0" encoding="UTF-8"?>
<root>
<item>
<CreationDate>2017-03-18</CreationDate>
<ExpiresDate>20170318</ExpiresDate>
</item>
<item>
<CreationDate>2017-03-09</CreationDate>
<ExpiresDate>20170309</ExpiresDate>
</item>
</root>