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

[andreasabel]

The following MWE was distilled from:

• https://github.com/agda/agda/issues/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