qed option without value fails in \declaretheoremstyle

[mbertucci47]

In thm-amsthm.sty, we have \define@key{thmdef}{qed}[\qedsymbol]{...} so if used without a value, the qed option should default to \qedsymbol. This works if used in \declaretheorem, but not if used in \declaretheoremstyle. Example:

\documentclass{article}
\usepackage{amsthm,thmtools}

% this fails
\declaretheoremstyle[qed]{mythmsty}
\declaretheorem[style=mythmsty]{theorem}
	
% this works
%\declaretheoremstyle[qed=\textdagger]{mythmsty}
%\declaretheorem[style=mythmsty]{theorem}

% this works
%\declaretheorem[qed]{theorem}

\begin{document}

\begin{theorem}
Text
\end{theorem}

\end{document}

Here's the full error:

! Argument of \strip@prefix has an extra }.
<inserted text> 
                \par 
l.5 \declaretheoremstyle[qed]{mythmsty}
                                       
I've run across a `}' that doesn't seem to match anything.
For example, `\def\a#1{...}' and `\a}' would produce
this error. If you simply proceed now, the `\par' that
I've just inserted will cause me to report a runaway
argument that might be the root of the problem. But if
your `}' was spurious, just type `2' and it will go away.

Runaway argument?
\relax
! Paragraph ended before \strip@prefix was complete.
<to be read again> 
                   \par 
l.5 \declaretheoremstyle[qed]{mythmsty}
                                       
I suspect you've forgotten a `}', causing me to apply this
control sequence to too much text. How can we recover?
My plan is to forget the whole thing and hope for the best.

Package thmtools Info: Key `qed' (with value `\par ')
(thmtools)             is not a known style key.
(thmtools)             Will pass this to every \declaretheorem
(thmtools)             that uses `style=mythmsty' on input line 5.