diff --git a/exec_apply_effects.lua b/exec_apply_effects.lua
index 6245ea5..5ba64ca 100644
--- a/exec_apply_effects.lua
+++ b/exec_apply_effects.lua
@@ -780,7 +780,7 @@ yl_speak_up.execute_effect = function(player, n_id, o_id, r)
 			local npc_inv = minetest.get_inventory({type="detached",
 				name="yl_speak_up_npc_"..tostring(n_id)})
 			-- put the drops into the inventory of the NPC
-			for i, d in ipairs(drop_list) do
+			for i, d in ipairs(drop_list or {}) do
 				local rest = npc_inv:add_item("npc_main", ItemStack(d))
 				if(rest and not(rest:is_empty()) and rest:get_count()>0) then
 					yl_speak_up.debug_msg(player, n_id, o_id, tostring(r.r_id)..
@@ -867,7 +867,7 @@ yl_speak_up.execute_effect = function(player, n_id, o_id, r)
 		input.items = {}
 		-- multiple slots in the craft grid may contain the same item
 		local sum_up = {}
-		for i, v in ipairs(r.r_craft_grid) do
+		for i, v in ipairs(r.r_craft_grid or {}) do
 			if(v and v ~= "") then
 				local stack = ItemStack(v)
 				-- store this for later crafting
@@ -913,7 +913,7 @@ yl_speak_up.execute_effect = function(player, n_id, o_id, r)
 		yl_speak_up.debug_msg(player, n_id, o_id, tostring(r.r_id).." "..
 				"Great: Crafting is possible!")
 		-- actually consume the items required, return the ones in decremented_input
-		for i, v in ipairs(r.r_craft_grid) do
+		for i, v in ipairs(r.r_craft_grid or {}) do
 			if(v and v ~= "") then
 				npc_inv:remove_item("npc_main", ItemStack(v))
 			end
@@ -925,7 +925,7 @@ yl_speak_up.execute_effect = function(player, n_id, o_id, r)
 		end
 		npc_inv:add_item("npc_main", output.item)
 		-- add the decremented_inputs
-		for k,v in pairs(decremented_input.items) do
+		for k,v in pairs(decremented_input.items or {}) do
 			if(k and not(v:is_empty())) then
 				if(not(npc_inv:room_for_item("npc_main", v))) then
 					yl_speak_up.debug_msg(player, n_id, o_id, tostring(r.r_id).." "..
diff --git a/exec_eval_preconditions.lua b/exec_eval_preconditions.lua
index 1176009..385dd14 100644
--- a/exec_eval_preconditions.lua
+++ b/exec_eval_preconditions.lua
@@ -74,7 +74,7 @@ yl_speak_up.eval_all_preconditions = function(player, prereq, o_id, other_option
 	-- during this call, so we can cache them
 	local properties = yl_speak_up.get_npc_properties(pname)
 
-	for k, p in pairs(prereq) do
+	for k, p in pairs(prereq or {}) do
 		yl_speak_up.debug_msg(player, n_id, o_id, "..checking "..
 			tostring(p.p_id)..": "..yl_speak_up.show_precondition(p, pname))
 		if(not(yl_speak_up.eval_precondition(player, n_id, p, other_options_true_or_false, properties))) then
@@ -465,7 +465,7 @@ yl_speak_up.eval_trade_list_preconditions = function(player)
 	for i, s_o_id in ipairs(sorted_o_list) do
 		local prereq = options[s_o_id].o_prerequisites
 		local all_ok = true
-		for k, p in pairs(prereq) do
+		for k, p in pairs(prereq or {}) do
 			if(not(yl_speak_up.eval_precondition_npc_inv(p, inv, inv_name))) then
 				all_ok = false
 				break