XSLT: Check if a string is null or empty.

check-null-empty.xsl

<!--
    CHECK IF A STRING IS NULL OR EMPTY
--> 

<!-- Example XML -->
<group> 
    <item> 
        <id>item 1</id> 
        <CategoryName>blue</CategoryName> 
    </item> 
    <item> 
        <id>item 2</id> 
        <CategoryName></CategoryName> 
    </item> 
    <item> 
        <id>item 3</id> 
    </item> 
</group>

<!-- Example test case -->
<xsl:for-each select="/group/item"> 
    <xsl:if test="CategoryName"> 
         <!-- will be instantiated for item #1 and item #2 -->
    </xsl:if> 
    <xsl:if test="not(CategoryName)"> 
        <!-- will be instantiated for item #3 -->
    </xsl:if> 
    <xsl:if test="CategoryName != ''"> 
        <!-- will be instantiated for item #1 -->
    </xsl:if> 
    <xsl:if test="CategoryName = ''"> 
        <!-- will be instantiated for item #2 -->
    </xsl:if> 
</xsl:for-each>

<!--
    To test if the value of a certain node is empty it depends on what is meant by empty.

    * Contains no child nodes: not(node()) 
    * Contains no text content: not(string(.)) 
    * Contains no text other than whitespace: not(normalize-space(.)) 
    * Contains nothing except comments: not(node()[not(self::comment())])
-->