If I println something it doesnt break

so I have a tool in an inventory, and every time the player uses it by mining, it updates the tool in the inventory. the tool in their hand has lore values, and I clear al the lore values before I give it back to the player.
the values are never actually cleared unless I print the inventory contents or something similar.

Code:

Inventory mtinv = toolinv.get(player.getUniqueId()); //create inventory of mtinv
                                            ItemStack handstack = player.getInventory().getItemInMainHand().clone();
                                            ItemMeta stackmeta = handstack.getItemMeta();
                                            stackmeta.setLore(null);
                                            handstack.setItemMeta(stackmeta);
                                            mtinv.setItem(i, handstack); //replace old item with used item
                                            System.out.println(mtinv.getContents());
                                            toolinv.put(player.getUniqueId(), mtinv); //replace old inv with new inv
                                            break;

if I dont include the print line, the lore stays on the tools

 

@timtower
the outside inventory still has the item lores in it now.

 

the player has an outside inventory

Code:

if (toolinv.containsKey(player.getUniqueId())) { //if the player's mt inv exists
                                    ItemStack givestack = new ItemStack(Material.AIR, 0);
                                    boolean chosentool = false;
                                    for (int i = 0; i < 5; i++) { //this loops through the mt inv, checks which index the current item being used is in, and then updates it
                                        if (toolinv.get(player.getUniqueId()).getItem(i).getType() == player.getInventory().getItemInMainHand().getType()) {
                                            Inventory mtinv = toolinv.get(player.getUniqueId()); //create inventory of mtinv
                                            ItemStack handstack = player.getInventory().getItemInMainHand().clone();
                                            ItemMeta stackmeta = handstack.getItemMeta();
                                            stackmeta.setLore(null);
                                            handstack.setItemMeta(stackmeta);
                                            mtinv.setItem(i, handstack); //replace old item with used item
                                            player.updateInventory();
                                            toolinv.put(player.getUniqueId(), mtinv); //replace old inv with new inv
                                            break;
                                        }
                                    }

there's the inventory inside a hashmap called toolinv, and then there's the players inventory

@timtower

EDIT by Moderator: merged posts, please use the edit button instead of double posting.