obscure error in index file

Question

I reduce my problem to the following example:

\documentclass{scrbook}
\usepackage[nochapters]{classicthesis}
\usepackage{tikz}
\usepackage{makeidx}

\makeindex

\begin{document}

\index{j}
\nocite{Salsa}

\begin{thebibliography}{1}
\bibitem{Salsa}
Salsa
\end{thebibliography}

\printindex

\end{document}

I compile the file with the command latexmk --pdf and get the following error:

! A <box> was supposed to be here.
<to be read again> 
                   \def 
l.5 \end{theindex}

line numbers referring to the ind generated file which reads as:

\begin{theindex}

  \item j, \hyperpage{1}

\end{theindex}

The error can be reproduced on the docker image: ghcr.io/xu-cheng/texlive-full