polytable 2020/07/14 v0.8.6 crashes with Package array Error: Empty preamble: `l' used.

[andreasabel]

The following MWE was distilled from:

• Latex backend/package bug: ! Package array Error: Empty preamble: 'l' used. agda/agda#7290

\documentclass{article}
\RequirePackage{polytable}
\defaultcolumn{l}
\begin{document}
%% The column names must be different
\begin{pboxed}\savecolumns
\\ %% needed
\>[foo]
\end{pboxed}
\begin{pboxed}\restorecolumns
\>[bar]
\end{pboxed}
\begin{pboxed}\restorecolumns
\>[baz]
\end{pboxed}
\end{document}

Running this through latex twice gives the following error:

! Package array Error: Empty preamble: `l' used.

[andreasabel]

ATTN: @kosmikus