Incompatibility of the options `numberwithin` and `numbered=unless unique`

[dbitouze]

The options numberwithin and numbered=unless unique are incompatible. Indeed the following MCE:

\documentclass{article}
\usepackage{amsthm}
\usepackage{thmtools}
\usepackage[unq]{unique}
%
\declaretheorem[numberwithin=section,numbered=unless unique]{singleton}
%
\begin{document}
\section{One}
\begin{singleton}
  Me
\end{singleton}
\end{document}

leads to:

! LaTeX Error: Missing \begin{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.23 ...section,numbered=unless unique]{singleton}