The logic is confused when I compile and decompile this code with lua 5.1.5 about luadec HOT 2 OPEN

function a (b)
  c = c or {}
  return b
end

-- Decompiled using luadec 2.2 rev: 705713f for Lua 5.1 from https://github.com/viruscamp/luadec
-- Command line: test1.lua

-- params : ...
-- function num : 0
a = function(b)
  -- function num : 0_0
  if not c then
    c = {}
    return b
  end
end