NullPointerException because "container" is null

[elgbar]

While testing fixes for #1, I stumbled upon an NPE.

This happened when I clicked the cast High Level Alchemy in the standard spell book. I had no explorer's ring on me, nor any runes.
The weird thing is that the widgets were correctly hidden.

[Client] ERROR n.r.client.callback.ClientThread - Exception in invoke
java.lang.NullPointerException: Cannot invoke "net.runelite.api.ItemContainer.contains(int)" because "container" is null
	at com.creativetechguy.NoBadAlchsPlugin.containsExplorerRing(NoBadAlchsPlugin.java:257)
	at com.creativetechguy.NoBadAlchsPlugin.isAlchCastPoweredByExplorerRing(NoBadAlchsPlugin.java:246)
	at com.creativetechguy.NoBadAlchsPlugin._hideItemsTask(NoBadAlchsPlugin.java:175)
	at com.creativetechguy.NoBadAlchsPlugin.lambda$queueSingleTask$0(NoBadAlchsPlugin.java:238)
	at net.runelite.client.callback.ClientThread.lambda$invokeAtTickEnd$2(ClientThread.java:94)
	at net.runelite.client.callback.ClientThread.invokeList(ClientThread.java:119)
	at net.runelite.client.callback.ClientThread.invokeTickEnd(ClientThread.java:106)
	at net.runelite.client.callback.Hooks.tickEnd(Hooks.java:249)
	at client.jl(client.java:57631)
	at client.bs(client.java:1164)
	at bm.ay(bm.java:401)
	at bm.run(bm.java:380)
	at java.base/java.lang.Thread.run(Thread.java:833)

[CreativeTechGuy]

Thanks for letting me know. I haven't seen this before. Is it reproducible or was it a one-off?