xmltask test existence of node without text or attribute

I'm using Ant 1.8.4 and xmltask 1.16. I'm trying to modify Maven pom.xml files to check if there is a /project/properties element and create one if there isn't (so that I can then add a child element). The xmltask documentation indicates I have to use the copy task to check, and then use the if attribute on the insert task. But using this code

<xmltask source="${pomdir}/pom.xml" dest=""${pomdir}/pom.xml">
  <copy path="/:project/:properties" property="hasProperties"/>
  <insert path="/:project/:packaging" position="after" if="hasProperties"
    xml="&lt;properties&gt;"/>
</xmltask>

Produces this warning when there is an existing /project/properties node

Can only copy/cut text() nodes and attribute values to properties (found com.sun.org.apache.xerces.internal.dom.DeferredElementNSImpl)

And it inserts a second properties node. Adding "/text()" to the end of the xpath in the copy task gets rid of the warning but doesn't fix the duplicated properties node in the output.

I found the solution. I have to conditionally select the project node that does not have a properties child node.

<insert path="/:project[not(:properties)]/:packaging"
    position="after">
    <![CDATA[
    <properties>
        <customProperty>blah</customProperty>
    </properties>
    ]]>
</insert>
<insert path="/:project/:properties"
    xml="&lt;customProperty&gt;blah&lt;/customProperty&gt;"/>

The first insert covers input files that have no properties, and the second insert covers input files that do already have properties.