[icyblade]

well i think i've figured it out
in TidyPlates\TidyPlatesCore.lua, Line 918:
the fact is in WoD, UnitExists(unit) will return true/false rather than 1/0, so we can just simply change

function events:PLAYER_TARGET_CHANGED() HasTarget = UnitExists("target") == 1; 	SetUpdateAll() 	end

to

function events:PLAYER_TARGET_CHANGED() HasTarget = UnitExists("target") == true; 	SetUpdateAll() 	end

then we have opacity back, so have debuff