Choose Test for Emtpy element

Hello,

I am performing a CHOOSE | WHERE | OTHERWISE ... the test for this choose is
to see whether or not my @AvailableInventory is '' (empty).  It doesn't seem
to work, but indeed there is no real value in this attribute.  I'm thinking
it is padded with spaces.  So how would I perform my test, but trim all the
spaces... or is there another test for "Empty"?
Here what I have so far:

  <xsl:when test="@availableInventory=''">
       <xsl:text>-</xsl:text><!-- returning a dash here -->
  </xsl:when>
  <xsl:otherwise>
         <xsl:text>$ </xsl:text>
       <xsl:value-of select="format-number(@AvailableInventory,'###,###')"/>
  </xsl:otherwise>
  </xsl:choose>


Thanks!

Karl


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