Minor Issue happens when running a plugin that freezes a player and the player tries to move, this is a private plugin however, after speaking to the developer, they stated that it was a Spigot bug and that it should be reported.
[14:33:12 FATAL]: Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.8.0]
at java.util.concurrent.FutureTask.get(FutureTask.java:192) ~[?:1.8.0]
at net.minecraft.server.v1_9_R1.SystemUtils.a(SourceFile:46) [spigot.jar:git-Spigot-dd155ed-31caee5]
at net.minecraft.server.v1_9_R1.MinecraftServer.D(MinecraftServer.java:721) [spigot.jar:git-Spigot-dd155ed-31caee5]
at net.minecraft.server.v1_9_R1.DedicatedServer.D(DedicatedServer.java:400) [spigot.jar:git-Spigot-dd155ed-31caee5]
at net.minecraft.server.v1_9_R1.MinecraftServer.C(MinecraftServer.java:660) [spigot.jar:git-Spigot-dd155ed-31caee5]
at net.minecraft.server.v1_9_R1.MinecraftServer.run(MinecraftServer.java:559) [spigot.jar:git-Spigot-dd155ed-31caee5]
at java.lang.Thread.run(Thread.java:744) [?:1.8.0]
Caused by: java.lang.NullPointerException
at net.minecraft.server.v1_9_R1.PlayerConnection.a(PlayerConnection.java:408) ~[spigot.jar:git-Spigot-dd155ed-31caee5]
at net.minecraft.server.v1_9_R1.PacketPlayInTeleportAccept.a(SourceFile:31) ~[spigot.jar:git-Spigot-dd155ed-31caee5]
at net.minecraft.server.v1_9_R1.PacketPlayInTeleportAccept.a(SourceFile:8) ~[spigot.jar:git-Spigot-dd155ed-31caee5]
at net.minecraft.server.v1_9_R1.PlayerConnectionUtils$1.run(SourceFile:13) ~[spigot.jar:git-Spigot-dd155ed-31caee5]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) ~[?:1.8.0]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0]
at net.minecraft.server.v1_9_R1.SystemUtils.a(SourceFile:45) ~[spigot.jar:git-Spigot-dd155ed-31caee5]
... 5 more
