NPE in varbitchanged subscriber caused extreme log spam

[Nightfirecat]

2021-11-10 12:13:47 [Client] DEBUG n.r.client.config.ConfigManager - Setting configuration value for kittenConfig.felineId to 1620
2021-11-10 12:13:47 [Client] WARN  n.runelite.client.eventbus.EventBus - Uncaught exception in event subscriber
java.lang.NullPointerException: null
	at java.base/java.time.Duration.between(Duration.java:488)
	at com.kittentracker.KittenPlugin.saveGrowthProgress(KittenPlugin.java:328)
	at com.kittentracker.KittenPlugin.byeFollower(KittenPlugin.java:268)
	at com.kittentracker.KittenPlugin.onVarbitChanged(KittenPlugin.java:191)
	at net.runelite.client.eventbus.EventBus$Subscriber.invoke(EventBus.java:70)
	at net.runelite.client.eventbus.EventBus.post(EventBus.java:223)
	at net.runelite.client.callback.Hooks.post(Hooks.java:169)
	at client.jy(client.java:56481)
	at client.ho(client.java:6136)
	at client.fc(client.java:3304)
	at client.h(client.java:1540)
	at ai.oz(ai.java:387)
	at ai.run(ai.java:366)
	at java.base/java.lang.Thread.run(Thread.java:829)