how to add condition which check xml data with lookup table - xslt

Question

I want to ask. there is posible to add condition which will be checking xml data with lookup table, and if we didnt't have value in lookup table add const 8 to output?
xslt Code:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:key name="Department" match="Department" use="../Collection"/>
<xsl:template match="/">
<document>
<xsl:apply-templates/>
</document>
</xsl:template>
<xsl:template match="line">
<xsl:variable name="inputDep" select="field[#id='3']"/>
<Department>
<xsl:for-each select="document('lookup.xml')">
<xsl:for-each select="key('Deparment',$inputDep)">
<xsl:value-of select="."/>
</xsl:for-each>
</xsl:for-each>
</Department>
</xsl:template>
</xsl:stylesheet>
lookup table:
<document>
<line-item>
<Collection>1</Collection>
<Department>3</Department>
</line-item>
<line-item>
<Collection>2</Collection>
<Department>1</Department>
</line-item>
<line-item>
<Collection>3</Collection>
<Department>2</Department>
</line-item>
</document>
xml file:
<document>
<line id="0">
<field id="3"><![CDATA[1]]></field>
</line>
<line id="1">
<field id="3"/>
</line>
<line id="2">
<field id="3"/><![CDATA[4]]></field>
</line>
</document>
result:
<Department>3<Department>
<Department>8<Department>
<Department>8<Department>

Answer 1

You could assign the looked-up value to a variable and choose what to output based on whether anything was found.
Edit 2: A full demonstration stylesheet:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:key name="Department" match="Department" use="../Collection"/>
<xsl:template match="/">
<document>
<xsl:apply-templates/>
</document>
</xsl:template>
<xsl:template match="line">
<xsl:variable name="inputDep" select="field[#id='3']"/>
<Department>
<xsl:for-each select="document('lookup.xml')">
<xsl:variable name="value" select="key('Department',$inputDep)"/>
<xsl:choose>
<xsl:when test="$value">
<xsl:value-of select="$value"/> <!-- see note -->
</xsl:when>
<xsl:otherwise>8</xsl:otherwise>
</xsl:choose>
</xsl:for-each>
</Department>
</xsl:template>
</xsl:stylesheet>
Note: Replaced the xsl:for-each loop in the original stylesheet with a simple xsl:value-of, assuming that the looping the values was not intentional. If it actually was, you can replace this with a for-each loop.