CSV::Parser::InputsScanner#keep_drop

# File tmp/rubies/ruby-3.3.0/lib/csv/parser.rb, line 227
def keep_drop
  _, _, buffer = @keeps.pop
  # trace(__method__, :done, :empty) unless buffer
  return unless buffer

  last_keep = @keeps.last
  # trace(__method__, :done, :no_last_keep) unless last_keep
  return unless last_keep

  if last_keep[2]
    last_keep[2] << buffer
  else
    last_keep[2] = buffer
  end
  # trace(__method__, :done)
end