Cant upgrade sword

**Describe the bug**
Cant upgrade item

**To Reproduce**
Steps to reproduce the behavior:

**Expected behavior**
Be able to update wepons in game. If you die it downgrade the iten from what youve bought, e.g. if youve bough a iron pickaxe, you will have a woden one, then if you die, it downgardes to the previous one and give you that

**Console Output**
```
[16:13:44 ERROR]: Could not pass event InventoryClickEvent to BedWars1058 v25.5-SNAPSHOT
java.lang.NullPointerException: Cannot invoke "String.equals(Object)" because the return value of "com.andrei1058.bedwars.api.server.VersionSupport.getShopUpgradeIdentifier(org.bukkit.inventory.ItemStack)" is null
at bedwars-plugin-25.5-SNAPSHOT.jar/com.andrei1058.bedwars.shop.ShopCache$CachedItem.upgrade(ShopCache.java:133) ~[bedwars-plugin-25.5-SNAPSHOT.jar:?]
at bedwars-plugin-25.5-SNAPSHOT.jar/com.andrei1058.bedwars.shop.ShopCache.upgradeCachedItem(ShopCache.java:189) ~[bedwars-plugin-25.5-SNAPSHOT.jar:?]
at bedwars-plugin-25.5-SNAPSHOT.jar/com.andrei1058.bedwars.shop.main.CategoryContent.execute(CategoryContent.java:188) ~[bedwars-plugin-25.5-SNAPSHOT.jar:?]
at bedwars-plugin-25.5-SNAPSHOT.jar/com.andrei1058.bedwars.shop.listeners.InventoryListener.onInventoryClick(InventoryListener.java:109) ~[bedwars-plugin-25.5-SNAPSHOT.jar:?]
at co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:80) ~[paper-api-1.21.4-R0.1-SNAPSHOT.jar:?]
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[paper-api-1.21.4-R0.1-SNAPSHOT.jar:?]
at io.papermc.paper.plugin.manager.PaperEventManager.callEvent(PaperEventManager.java:54) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at io.papermc.paper.plugin.manager.PaperPluginManagerImpl.callEvent(PaperPluginManagerImpl.java:131) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:628) ~[paper-api-1.21.4-R0.1-SNAPSHOT.jar:?]
at net.minecraft.server.network.ServerGamePacketListenerImpl.handleContainerClick(ServerGamePacketListenerImpl.java:3209) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.network.protocol.game.ServerboundContainerClickPacket.handle(ServerboundContainerClickPacket.java:69) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.network.protocol.game.ServerboundContainerClickPacket.handle(ServerboundContainerClickPacket.java:14) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.network.protocol.PacketUtils.lambda$ensureRunningOnSameThread$0(PacketUtils.java:29) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.server.TickTask.run(TickTask.java:18) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.util.thread.BlockableEventLoop.doRunTask(BlockableEventLoop.java:155) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.util.thread.ReentrantBlockableEventLoop.doRunTask(ReentrantBlockableEventLoop.java:24) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:1448) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:176) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.util.thread.BlockableEventLoop.pollTask(BlockableEventLoop.java:129) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.server.MinecraftServer.pollTaskInternal(MinecraftServer.java:1428) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.server.MinecraftServer.pollTask(MinecraftServer.java:1422) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.util.thread.BlockableEventLoop.managedBlock(BlockableEventLoop.java:139) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.server.MinecraftServer.managedBlock(MinecraftServer.java:1379) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.server.MinecraftServer.waitUntilNextTick(MinecraftServer.java:1387) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1264) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at net.minecraft.server.MinecraftServer.lambda$spin$2(MinecraftServer.java:310) ~[paper-1.21.4.jar:1.21.4-231-09e9afd]
at java.base/java.lang.Thread.run(Thread.java:1583) ~[?:?]
```

**System (please complete the following information):**
- OS: Linux (docker)
- Server software Paper
- Server Version 1.21.4
- Plugin Version 25.5-SNAPSHOT