Replace blank rows

My xml is as follows:
<row>
 <column name="firstname">K1</column>
 <column name="lastname">L1</column
</row>
<row>                               --> Empty Row contains empty cells
 <column name="firstname></column>  --> These should be replaced by
 <column name="lastname></column>   --> "K1" and "L1" from prev. row.
</row>
<row>                                --> Empty row again.
 <column name="firstname></column>
 <column name="lastname></column>
</row>
....

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 version="1.0">

 <xsl:choose>
   <xsl:when test="$STR != ''">
     <xsl:copy-of select="."/>
   </xsl:when>
   <xsl:when test="$STR = '' and position() > 0 and $fillCell = 'Y'">
     <xsl:variable name="pos" select="position() -1"/>
        <xsl:copy-of select="//Document/row[$pos]"/>
   </xsl:when>
 </xsl:choose>

</xsl:for-each>
</Document>

<xsl:template match="text()" mode="row">
<xsl:value-of select="."/>
</xsl:template>