Not the child false but the value false()

Saxon produces an error message, e.g.,

wadl-stylesheet$ java -jar /Applications/SaxonHE9-6-0-1J/saxon9he.jar -s:example_wadl.xml -xsl:wadl.xsl -o:example_wadl.html
Warning: at xsl:when on line 461 column 93 of wadl.xsl:
  in {...tp://www.w3.org/XML/') = fa...}:
    The expression is looking for a child element named 'false' - perhaps false() was
  intended? To avoid this warning, use child::false or ./false