Empty captions with KOMA-script

Question

I like captions to normally have a colon, but not when the caption is empty. This is something that the package caption does automatically, so

\documentclass{scrartcl}
\usepackage{caption}
\begin{document}
\begin{figure}
  \caption{Test}
  \caption{}
\end{figure}
\end{document}

yields "Figure 1: Test / Figure 2". That is all very fine, but I want to use KOMA captions without the caption package, and then I get "Figure 1: Test / Figure 2:" with the extra colon at the end.

Here is my best try in fixing this, but it doesn't work. How can I do instead?

\documentclass{scrartcl}
\usepackage{xifthen}
\makeatletter
\renewcommand{\scr@@makesinglelinecaption}[3]{%
    \usekomafont{caption}{\strut\ignorespaces
      #1{{\usekomafont{captionlabel}{#2\ifthenelse{\isempty{#3}}{}{\captionformat}}}}%
      \ignorespaces #3\unskip}%
}
\makeatother

\begin{document}
\begin{figure}
  \caption{Test}
  \caption{}
\end{figure}
\end{document}

Answer 1

Your test doesn't work as KOMA doesn't pass an empty argument, it contains (for an unknown reason) \ignorespaces, so you should test for this:

\documentclass{scrartcl}
\usepackage{expl3,xpatch}
\ExplSyntaxOn
\makeatletter
\patchcmd\scr@@makesinglelinecaption{\captionformat}
 {\tl_if_eq:nnF {\ignorespaces}{#3}{\captionformat}}{}{\fail}
\ExplSyntaxOff

%\usepackage{caption}
\begin{document}
\begin{figure}
  \caption{Test}
  \caption{}
\end{figure}
\end{document}