Not directly addressing your question, but perhaps avoidance is an option?

my @headings2 = map { { key => $_->[0], name => $_->[1], class => $_->
+[2] } }
  #--  KEY    NAME          CLASS   ----
  [ qw(k      Kanji         kanji    ) ],
  [ qw(skip   SKIP          skip-code) ],
  [ qw(co     Suggestion    skip-code) ],
  [ qw(disc   Discussion),  undef      ];
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The difference between your AoH and @headings2 is, that $heading2[3]->{class} exists and is undef. My Emacs (cperl-mode) does not re-indent this block.