Inventory command error

java.lang.ClassCastException: com.google.common.collect.RegularImmutableMap cannot be cast to org.spongepowered.api.item.inventory.ItemStack
	at com.rysingdragon.novaprime.inventories.Backpack.loadInventory(Backpack.java:56) ~[Backpack.class:?]
	at com.rysingdragon.novaprime.inventories.Backpack.<init>(Backpack.java:44) ~[Backpack.class:?]
	at com.rysingdragon.novaprime.commands.SpongeBackpackCommand.execute(SpongeBackpackCommand.java:25) ~[SpongeBackpackCommand.class:?]
	at com.rysingdragon.novaprime.commands.CommandBase.process(CommandBase.java:47) ~[CommandBase.class:?]
	at org.spongepowered.api.command.dispatcher.SimpleDispatcher.process(SimpleDispatcher.java:333) ~[SimpleDispatcher.class:1.10.2-2202-5.1.0-BETA-2100]
	at org.spongepowered.common.command.SpongeCommandManager.process(SpongeCommandManager.java:295) [SpongeCommandManager.class:1.10.2-2202-5.1.0-BETA-2100]
	at net.minecraft.command.ServerCommandManager.func_71556_a(SourceFile:1083) [bd.class:?]
	at net.minecraft.network.NetHandlerPlayServer.func_147361_d(NetHandlerPlayServer.java:913) [me.class:?]
	at net.minecraft.network.NetHandlerPlayServer.func_147354_a(NetHandlerPlayServer.java:892) [me.class:?]
	at net.minecraft.network.play.client.CPacketChatMessage.func_148833_a(SourceFile:37) [im.class:?]
	at net.minecraft.network.play.client.CPacketChatMessage.func_148833_a(SourceFile:9) [im.class:?]
	at org.spongepowered.common.network.PacketUtil.onProcessPacket(PacketUtil.java:156) [PacketUtil.class:1.10.2-2202-5.1.0-BETA-2100]
	at net.minecraft.network.PacketThreadUtil$1.redirect$onProcessPacket$zje000(SourceFile:539) [fl$1.class:?]
	at net.minecraft.network.PacketThreadUtil$1.run(SourceFile:13) [fl$1.class:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.8.0_91]
	at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.8.0_91]
	at net.minecraft.util.Util.func_181617_a(SourceFile:45) [h.class:?]
	at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:668) [MinecraftServer.class:?]
	at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:387) [ld.class:?]
	at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:613) [MinecraftServer.class:?]
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:471) [MinecraftServer.class:?]
	at java.lang.Thread.run(Unknown Source) [?:1.8.0_91]