Exceptions in Events manager

[NiklasEi]

deadfish on Discord
I'm having some console errors sometimes after the event. I'm using the listener in the plugin. The event was triggered correctly but there's this error after some time. Do you have any idea what is causing this? Thanks!

[15:38:49] [Server thread/WARN]: [CalendarEvents] Task #4102869 for CalendarEvents v2.3.0 generated an exception
java.lang.NullPointerException: null
    at me.nikl.calendarevents.EventsManager.callEvent(EventsManager.java:358) ~[?:?]
    at me.nikl.calendarevents.EventsManager.access$100(EventsManager.java:30) ~[?:?]
    at me.nikl.calendarevents.EventsManager$3$1.run(EventsManager.java:425) ~[?:?]
    at org.bukkit.craftbukkit.v1_16_R3.scheduler.CraftTask.run(CraftTask.java:99) ~[patched_1.16.4.jar:git-Paper-345]
    at org.bukkit.craftbukkit.v1_16_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:468) ~[patched_1.16.4.jar:git-Paper-345]
    at net.minecraft.server.v1_16_R3.MinecraftServer.b(MinecraftServer.java:1294) ~[patched_1.16.4.jar:git-Paper-345]
    at net.minecraft.server.v1_16_R3.DedicatedServer.b(DedicatedServer.java:377) ~[patched_1.16.4.jar:git-Paper-345]
    at net.minecraft.server.v1_16_R3.MinecraftServer.a(MinecraftServer.java:1209) ~[patched_1.16.4.jar:git-Paper-345]
    at net.minecraft.server.v1_16_R3.MinecraftServer.w(MinecraftServer.java:997) ~[patched_1.16.4.jar:git-Paper-345]
    at net.minecraft.server.v1_16_R3.MinecraftServer.lambda$a$0(MinecraftServer.java:178) ~[patched_1.16.4.jar:git-Paper-345]
    at java.lang.Thread.run(Thread.java:832) [?:?]

And there's one time when the actions couldn't run successfully with the following error.

[15:45:06] [Server thread/WARN]: [CalendarEvents] Task #4219253 for CalendarEvents v2.3.0 generated an exception
java.util.ConcurrentModificationException: null
    at java.util.HashMap$Values.forEach(HashMap.java:1071) ~[?:?]
    at me.nikl.calendarevents.EventsManager.reCalcNextMillis(EventsManager.java:435) ~[?:?]
    at me.nikl.calendarevents.scheduling.Timer$1$1.run(Timer.java:29) ~[?:?]
    at org.bukkit.craftbukkit.v1_16_R3.scheduler.CraftTask.run(CraftTask.java:99) ~[patched_1.16.4.jar:git-Paper-345]
    at org.bukkit.craftbukkit.v1_16_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:468) ~[patched_1.16.4.jar:git-Paper-345]
    at net.minecraft.server.v1_16_R3.MinecraftServer.b(MinecraftServer.java:1294) ~[patched_1.16.4.jar:git-Paper-345]
    at net.minecraft.server.v1_16_R3.DedicatedServer.b(DedicatedServer.java:377) ~[patched_1.16.4.jar:git-Paper-345]
    at net.minecraft.server.v1_16_R3.MinecraftServer.a(MinecraftServer.java:1209) ~[patched_1.16.4.jar:git-Paper-345]
    at net.minecraft.server.v1_16_R3.MinecraftServer.w(MinecraftServer.java:997) ~[patched_1.16.4.jar:git-Paper-345]
    at net.minecraft.server.v1_16_R3.MinecraftServer.lambda$a$0(MinecraftServer.java:178) ~[patched_1.16.4.jar:git-Paper-345]
    at java.lang.Thread.run(Thread.java:832) [?:?]