[xsl] Check the variable value

[John Robb <john_ok@xxxxxx>]

How is it possible to check if the variable has some value or not.The 
variable value is text.

<xsl:variable name="image" select="IMAGE"/>
<xsl:if test="@image = null ">
  <xsl:text>asfa</xsl:text>
</xsl:if>

<TOPIC>
    <TITLE>Google</TITLE>
    <URL>http://www.eggheadcafe.com/default.asp</URL>
    <IMAGE>images/model-icon.gif</IMAGE>
  </TOPIC>
  <TOPIC>
    <TITLE>Actions</TITLE>
    <URL>http://www.eggheadcafe.com/forums.asp</URL>
    <IMAGE></IMAGE>
  </TOPIC>