Macro: Storage and usage of abstract content does not work in cls

I got handed a cls to use for in a document which produces an ! Undefined control sequence error when used with pdfTeX, Version 3.141592653-2.6-1.40.22 (MiKTeX 21.3)

! Undefined control sequence.
@maketitle ...ace {z@ }}end {center}@abstract 
                                                  vspace {3.0em}par vskip...

I tried narrowing the problem down and created a simplified cls and a corresponding MWE.

The creator of the class seems to try to grab the content of the abstract and store it for use in a modified maketitle command. The approach is similar to the one described here.

I tried several approaches but was unable to fix the error. Any ideas?

---

cls

ProvidesClass{test}[2021/03/22 v0.1 Test class]

% Set up basic geometry
LoadClass[10pt,a4paper,parskip=half]{scrartcl}

% Define title
lettest@maketitlemaketitle
renewcommand{maketitle}{
  twocolumn[
    test@maketitle
    large%
    begin{center}{%
      bfseries abstractnamevspace{-0.7em}vspace{z@}%
    }end{center}%
    @abstract%
    vspace{3.0em}%
  ]
  thispagestyle{empty}
}

% Change title command
renewcommand{@maketitle}{%
  begin{center}%
    letfootnotethanks%
    {%
      Largebfseries%
      expandafteruppercaseexpandafter{@title}%
      par%
    }%
    vskip 1.5em%
    {%
      Largelineskip .5em%
      begin{tabular}[t]{c}%
        @author%
      end{tabular}%
      par%
    }%
    vskip 1em%
    {%
      large@date%
    }%
  end{center}%
  parvskip 1.5em%
}

% Renew abstract command to store the abstract
renewcommand{abstract}[1]{
  def@abstract{#1}
}

MWE

documentclass{test}

usepackage{lipsum}

title{MWE}
author{raedma}

begin{document}

maketitle

begin{abstract}
lipsum[1]
end{abstract}

section{Introduction}
lipsum[1]

end{document}

abstract{This is the text of the abstract}

documentclass{test}

usepackage{lipsum}

title{MWE}
author{raedma}
abstract{lipsum[1]}

begin{document}

maketitle

section{Introduction}
lipsum[1]

end{document}