empty group in keyval should return empty value

[xworld21]

Example:

\documentclass{article}

\usepackage{keyval}
\makeatletter
\define@key{createvalue}{empty}{\def\myempty{#1}}
\setkeys{createvalue}{empty={}}

\begin{document}
  \ifx\myempty\@empty Empty.\else Not empty.\fi
\end{document}

LaTeX returns 'Empty', LaTeXML gives 'Not empty'.