Error Log

[05:26:29 ERROR]: Could not pass event PlayerInteractEvent to Practice v0.1b
org.bukkit.event.EventException
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:302) ~[spigot.jar:git-Spigot-1649]
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[spigot.jar:git-Spigot-1649]
        at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:514) [spigot.jar:git-Spigot-1649]
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:499) [spigot.jar:git-Spigot-1649]
        at org.bukkit.craftbukkit.v1_7_R4.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:242) [spigot.jar:git-Spigot-1649]
        at org.bukkit.craftbukkit.v1_7_R4.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:212) [spigot.jar:git-Spigot-1649]
        at net.minecraft.server.v1_7_R4.PlayerConnection.a(PlayerConnection.java:636) [spigot.jar:git-Spigot-1649]
        at net.minecraft.server.v1_7_R4.PacketPlayInBlockPlace.a(PacketPlayInBlockPlace.java:50) [spigot.jar:git-Spigot-1649]
        at net.minecraft.server.v1_7_R4.PacketPlayInBlockPlace.handle(PacketPlayInBlockPlace.java:86) [spigot.jar:git-Spigot-1649]
        at net.minecraft.server.v1_7_R4.NetworkManager.a(NetworkManager.java:186) [spigot.jar:git-Spigot-1649]
        at net.minecraft.server.v1_7_R4.ServerConnection.c(ServerConnection.java:81) [spigot.jar:git-Spigot-1649]
        at net.minecraft.server.v1_7_R4.MinecraftServer.v(MinecraftServer.java:734) [spigot.jar:git-Spigot-1649]
        at net.minecraft.server.v1_7_R4.DedicatedServer.v(DedicatedServer.java:289) [spigot.jar:git-Spigot-1649]
        at net.minecraft.server.v1_7_R4.MinecraftServer.u(MinecraftServer.java:584) [spigot.jar:git-Spigot-1649]
        at net.minecraft.server.v1_7_R4.MinecraftServer.run(MinecraftServer.java:490) [spigot.jar:git-Spigot-1649]
        at net.minecraft.server.v1_7_R4.ThreadServerApplication.run(SourceFile:628) [spigot.jar:git-Spigot-1649]
Caused by: java.lang.NullPointerException
        at fr.practice.guis.RankedGUI.openGUI(RankedGUI.java:36) ~[?:?]
        at fr.practice.events.onInteract.PlayerInteract(onInteract.java:71) ~[?:?]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_131]
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_131]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_131]
        at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_131]
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:298) ~[spigot.jar:git-Spigot-1649]
        ... 15 more