Need a quick help.

I have a text string called questionHeading, In my xslt I need to hide when this field is empty, I know we need to use the if statement, but not sure how to do it.

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE xsl:stylesheet [ <!ENTITY nbsp "&#x00A0;"> ]>
<xsl:stylesheet 
  version="1.0" 
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
  xmlns:msxml="urn:schemas-microsoft-com:xslt" 
  xmlns:umbraco.library="urn:umbraco.library" xmlns:Exslt.ExsltCommon="urn:Exslt.ExsltCommon" xmlns:Exslt.ExsltDatesAndTimes="urn:Exslt.ExsltDatesAndTimes" xmlns:Exslt.ExsltMath="urn:Exslt.ExsltMath" xmlns:Exslt.ExsltRegularExpressions="urn:Exslt.ExsltRegularExpressions" xmlns:Exslt.ExsltStrings="urn:Exslt.ExsltStrings" xmlns:Exslt.ExsltSets="urn:Exslt.ExsltSets" xmlns:CWS.Twitter="urn:CWS.Twitter" xmlns:umbraco.contour="urn:umbraco.contour" xmlns:PS.XSLTsearch="urn:PS.XSLTsearch" 
  exclude-result-prefixes="msxml umbraco.library Exslt.ExsltCommon Exslt.ExsltDatesAndTimes Exslt.ExsltMath Exslt.ExsltRegularExpressions Exslt.ExsltStrings Exslt.ExsltSets CWS.Twitter umbraco.contour PS.XSLTsearch ">

<xsl:output method="xml" omit-xml-declaration="yes"/>

<xsl:param name="currentPage"/>

<xsl:template match="/">

<!-- The fun starts here -->
<div class="faqs">
<xsl:for-each select="$currentPage/* [@isDoc and string(umbracoNaviHide) != '1']">

<!-- I NEED TO HIDE THIS CONTENT WHEN UMBRACO FIELD IS EMPTY -->
<h2><xsl:value-of select="questionHeading"/></h2>
</xsl:if>

<!-- TILL HERE -->

<h3><xsl:value-of select="question" disable-output-escaping="yes"/></h3>
<div><p><xsl:value-of select="answer" disable-output-escaping="yes"/></p></div>
</xsl:for-each>
</div>

</xsl:template>

</xsl:stylesheet>