Xml & xslt

Here are the XML elements

Code:

<element name="LastTimeBuyDate" type="dateTime" nillable="true"/> <element name="LastTimeDeliveryDate" type="dateTime" nillable="true"/>

What I am trying to do in XSLT is state that when the lasttimebuydate is empty to add the "nillable="true"" to the xml output... same thing for lasttimedeliovery date

Code:

<cim:LastTimeBuyDate><xsl:value-of select="ecim:LAST_TIME_BUY_DATE"/></cim:LastTimeBuyDate> <cim:LastTimeDeliveryDate><xsl:value-of select="ecim:LAST_TIME_DELIVERY_DATE"/></cim:LastTimeDeliveryDate>

basically I want the xsl to add an xsi:nil="true" to the xsl value of select so output could be something like

<LAST_TIME_BUY_DATE xsi:nil="true"/>