Always return the ItemStack for on_rightclick to comply with the API.

computer/computers.lua

@@ -29,6 +29,7 @@ minetest.register_node("computer:vanio", {
 	on_rightclick = function(pos, node, clicker, itemstack)
 		node.name = "computer:vanio_off"
 		minetest.set_node(pos, node)
+		return itemstack
 	end
 })
 
@@ -48,6 +49,7 @@ minetest.register_node("computer:vanio_off", {
 	on_rightclick = function(pos, node, clicker, itemstack)
 		node.name = "computer:vanio"
 		minetest.set_node(pos, node)
+		return itemstack
 	end
 })
 
@@ -168,6 +170,7 @@ minetest.register_node("computer:monitor", {
 	on_rightclick = function(pos, node, clicker, itemstack)
 		node.name = "computer:monitor_on"
 		minetest.set_node(pos, node)
+		return itemstack
 	end
 })
 
@@ -186,6 +189,7 @@ minetest.register_node("computer:monitor_on", {
 	on_rightclick = function(pos, node, clicker, itemstack)
 		node.name = "computer:monitor"
 		minetest.set_node(pos, node)
+		return itemstack
 	end
 })
 
@@ -294,12 +298,13 @@ minetest.register_node("computer:server", {
 	on_rightclick = function(pos, node, clicker, itemstack)
 		node.name = "computer:server_on"
 		minetest.set_node(pos, node)
+		return itemstack
 	end,
 	on_place = function(itemstack, placer, pointed_thing)
 		local pos = pointed_thing.above
 		if minetest.get_node({x=pos.x, y=pos.y+1, z=pos.z}).name ~= "air" then
 			minetest.chat_send_player( placer:get_player_name(), "Not enough vertical space to place a server!" )
-			return
+			return itemstack
 		end
 		return minetest.item_place(itemstack, placer, pointed_thing)
 	end
@@ -333,5 +338,6 @@ minetest.register_node("computer:server_on", {
 	on_rightclick = function(pos, node, clicker, itemstack)
 		node.name = "computer:server"
 		minetest.set_node(pos, node)
+		return itemstack
 	end
 })

computer/init.lua

@@ -27,11 +27,12 @@ computer.register = function (name, def)
 		node_box = def.node_box,
 		selection_box = def.node_box,
 		on_rightclick = function (pos, node, clicker, itemstack)
-			if (def.on_turn_off) then
-				if (def.on_turn_off(pos, node, clicker, itemstack)) then return end
+			if def.on_turn_off and def.on_turn_off(pos, node, clicker, itemstack) then
+				return itemstack
 			end
 			node.name = OFFSTATE
 			minetest.set_node(pos, node)
+			return itemstack
 		end
 	})
 	minetest.register_node(OFFSTATE, {
@@ -50,11 +51,12 @@ computer.register = function (name, def)
 		node_box = def.node_box_off or def.node_box,
 		selection_box = def.node_box_off or def.node_box,
 		on_rightclick = function (pos, node, clicker, itemstack)
-			if (def.on_turn_on) then
-				if (def.on_turn_on(pos, node, clicker, itemstack)) then return end
+			if def.on_turn_on and def.on_turn_on(pos, node, clicker, itemstack) then
+				return itemstack
 			end
 			node.name = ONSTATE
 			minetest.set_node(pos, node)
+			return itemstack
 		end,
 		drop = ONSTATE
 	})

computer/tetris.lua

@@ -276,7 +276,8 @@ minetest.register_node("computer:tetris_arcade", {
 		end
 		if minetest.get_node({x=pos.x, y=pos.y+1, z=pos.z}).name ~= "air" then
 			minetest.chat_send_player(placer:get_player_name(), "No room for place the Arcade!")
-		return end
+			return itemstack
+		end
 		local dir = placer:get_look_dir()
 		local node = {name="computer:tetris_arcade", param1=0, param2 = minetest.dir_to_facedir(dir)}
 		minetest.set_node(pos, node)