`\unless\ifcsname ...\endcsname` fails with "Missing `\endcsname`"

[muzimuzhi]

\documentclass{article}
\usepackage{unravel}
\unravel{\unless\ifcsname abc\endcsname\fi}

\begin{document}
\end{document}

||
|> \unless \ifcsname abc\endcsname \fi

[===== Step 1 =====] \unless = \unless
|| \reverse_if:N \ifcsname
|> abc\endcsname \fi

[===== Step 2 =====] \endcsname
|| \reverse_if:N \ifcsname abc\endcsname
|> \fi

! Missing \endcsname inserted.
<to be read again>
                   \__kernel_tl_set:Nx
l.3 \unravel{\unless\ifcsname abc\endcsname\fi}

[PhelypeOleinik]

Duplicate of #50: fixed but not released yet, it seems

[muzimuzhi]

Oh yes! Why didn't I find it myself yesterday, even I must have read #50 before. Thank you a lot, Phelype.

PS: I confirm this is fixed, by cloning into local repo and running l3build install.