Yeah, but its filtered for crafting machine, which does have that key

for _, entity in pairs(game.get_filtered_entity_prototypes({{filter = "crafting-machine"}})) do
if entity.energy_source == "burner" and need_fuel(entity) == false then
_fuel_list[entity.name] = _fuel
end
Kmachine[entity.name] = true
end

the above code causes the error "LuaEntityPrototype ...