empty for body causes parsing errors

[amylizzle]

if (!contents_changed)
	return src.cached_producibility_data
for (var/obj/item/material_piece/M as anything in C)
// the body was not indented properly
var/list/output = list()
for (var/datum/manufacture/M as anything in ALL_BLUEPRINTS)
	var/M_ref = "\ref[M]"
	output[M_ref] = 1

this code threw unknown identifier errors on output. I'm pretty sure the empty for loop is eating the var def.

ideal output should probably be a warning on the empty for loop