skript error

> [15:24:38 INFO]: [Skript] Enabling Skript v2.4-beta5
> [15:24:41 ERROR]: Error occurred while enabling Skript v2.4-beta5 (Is it up to date?)
java.lang.ExceptionInInitializerError: null
at ch.njol.skript.aliases.Aliases.<clinit>(Aliases.java:142) ~[?:?]
at ch.njol.skript.Skript.onEnable(Skript.java:402) ~[?:?]
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:264) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:337) [server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:403) [server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.craftbukkit.v1_12_R1.CraftServer.enablePlugin(CraftServer.java:381) [server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.craftbukkit.v1_12_R1.CraftServer.enablePlugins(CraftServer.java:330) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.MinecraftServer.t(MinecraftServer.java:422) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.MinecraftServer.l(MinecraftServer.java:383) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.MinecraftServer.a(MinecraftServer.java:338) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.DedicatedServer.init(DedicatedServer.java:272) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:545) [server.jar:git-Spigot-dcd1643-e60fc34]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_212]
Caused by: java.lang.IllegalArgumentException: No enum constant org.bukkit.Material.OAK_PLANKS
at java.lang.Enum.valueOf(Enum.java:238) ~[?:1.8.0_212]
at org.bukkit.Material.valueOf(Material.java:1) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at ch.njol.skript.aliases.MaterialRegistry.load(MaterialRegistry.java:61) ~[?:?]
at ch.njol.skript.aliases.ItemData.<clinit>(ItemData.java:104) ~[?:?]
... 13 more