Can not change the category icon

[elytraByte]

uoe.txt

Describe the bug

Attempting to change a category's icon, an UnsupportedOperationException is thrown and the user is unable to pick or set a new icon.

To Reproduce

Open the main market's gui and navigate to your shop and then click on a category or create one. Click to enter the category. Inside the category's menu, click the change icon chest "button". Causes an UnsupportedOperationException and fails to allow you to change the category's icon.

Expected behavior
When you click the change icon chest "button" you should be able to pick an icon with left click and set one with right click.

Screenshots
If applicable, add screenshots to help explain your problem.

Server Information (please complete the following information):

• Server Version: 1.21.10
• Server Jar: Purpur - 1.21.10-2526-HEAD@75b794a
• Markets version: 2.38.1

Additional context

[16:25:23 ERROR]: Could not pass event InventoryClickEvent to Markets v2.38.1
java.lang.UnsupportedOperationException: null
at java.base/java.util.ImmutableCollections.uoe(ImmutableCollections.java:142) ~[?:?]
at java.base/java.util.ImmutableCollections$AbstractImmutableCollection.add(ImmutableCollections.java:147) ~[?:?]
at Markets - v2.38.1.jar/ca.tweetzy.markets.flight.gui.template.MaterialPickerGUI.draw(MaterialPickerGUI.java:91) ~[Markets - v2.38.1.jar:?]
at Markets - v2.38.1.jar/ca.tweetzy.markets.flight.gui.template.MaterialPickerGUI.(MaterialPickerGUI.java:64) ~[Markets - v2.38.1.jar:?]
at Markets - v2.38.1.jar/ca.tweetzy.markets.gui.shared.selector.ItemSelectorGUI.(ItemSelectorGUI.java:23) ~[Markets - v2.38.1.jar:?]
at Markets - v2.38.1.jar/ca.tweetzy.markets.gui.user.category.MarketCategoryEditGUI.lambda$drawIconButton$15(MarketCategoryEditGUI.java:213) ~[Markets - v2.38.1.jar:?]
at Markets - v2.38.1.jar/ca.tweetzy.markets.flight.gui.Gui.onClick(Gui.java:667) ~[Markets - v2.38.1.jar:?]
at Markets - v2.38.1.jar/ca.tweetzy.markets.flight.gui.GuiManager$GuiListener.onClickGUI(GuiManager.java:233) ~[Markets - v2.38.1.jar:?]
at co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:80) ~[purpur-api-1.21.10-R0.1-SNAPSHOT.jar:?]
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:71) ~[purpur-api-1.21.10-R0.1-SNAPSHOT.jar:?]
at io.papermc.paper.plugin.manager.PaperEventManager.callEvent(PaperEventManager.java:54) ~[purpur-1.21.10.jar:1.21.10-2526-75b794a]
at io.papermc.paper.plugin.manager.PaperPluginManagerImpl.callEvent(PaperPluginManagerImpl.java:131) ~[purpur-1.21.10.jar:1.21.10-2526-75b794a]
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:628) ~[purpur-api-1.21.10-R0.1-SNAPSHOT.jar:?]
at net.minecraft.server.network.ServerGamePacketListenerImpl.handleContainerClick(ServerGamePacketListenerImpl.java:3309) ~[purpur-1.21.10.jar:1.21.10-2526-75b794a]
at net.minecraft.network.protocol.game.ServerboundContainerClickPacket.handle(ServerboundContainerClickPacket.java:59) ~[purpur-1.21.10.jar:1.21.10-2526-75b794a]
at net.minecraft.network.protocol.game.ServerboundContainerClickPacket.handle(ServerboundContainerClickPacket.java:14) ~[purpur-1.21.10.jar:1.21.10-2526-75b794a]
at net.minecraft.network.PacketProcessor$ListenerAndPacket.handle(PacketProcessor.java:99) ~[purpur-1.21.10.jar:1.21.10-2526-75b794a]
at net.minecraft.network.PacketProcessor.executeSinglePacket(PacketProcessor.java:33) ~[purpur-1.21.10.jar:1.21.10-2526-75b794a]
at net.minecraft.server.MinecraftServer.pollTask(MinecraftServer.java:1538) ~[purpur-1.21.10.jar:1.21.10-2526-75b794a]
at net.minecraft.server.MinecraftServer.recordTaskExecutionTimeWhileWaiting(MinecraftServer.java:1244) ~[purpur-1.21.10.jar:1.21.10-2526-75b794a]
at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1379) ~[purpur-1.21.10.jar:1.21.10-2526-75b794a]
at net.minecraft.server.MinecraftServer.lambda$spin$2(MinecraftServer.java:388) ~[purpur-1.21.10.jar:1.21.10-2526-75b794a]
at java.base/java.lang.Thread.run(Thread.java:1583) ~[?:?]