Prism Error

[19:05:16] [Server thread/ERROR]: Could not pass event BlockSpreadEvent to Prism v2.0.4-18
org.bukkit.event.EventException
    at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:310) ~[spigot-1.8.7.jar:git-Spigot-6d0ae89-a03743b]
    at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[spigot-1.8.7.jar:git-Spigot-6d0ae89-a03743b]
    at me.Incomprehendable.WorldPlugins.FakePluginManager.fireEvent(FakePluginManager.java:138) [PerWorldPlugins.jar:?]
    at me.Incomprehendable.WorldPlugins.FakePluginManager.callEvent(FakePluginManager.java:124) [PerWorldPlugins.jar:?]
    at net.minecraft.server.v1_8_R3.BlockGrass.b(BlockGrass.java:61) [spigot-1.8.7.jar:git-Spigot-6d0ae89-a03743b]
    at net.minecraft.server.v1_8_R3.Block.a(Block.java:299) [spigot-1.8.7.jar:git-Spigot-6d0ae89-a03743b]
    at net.minecraft.server.v1_8_R3.WorldServer.h(WorldServer.java:495) [spigot-1.8.7.jar:git-Spigot-6d0ae89-a03743b]
    at net.minecraft.server.v1_8_R3.WorldServer.doTick(WorldServer.java:253) [spigot-1.8.7.jar:git-Spigot-6d0ae89-a03743b]
    at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:773) [spigot-1.8.7.jar:git-Spigot-6d0ae89-a03743b]
    at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:367) [spigot-1.8.7.jar:git-Spigot-6d0ae89-a03743b]
    at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:657) [spigot-1.8.7.jar:git-Spigot-6d0ae89-a03743b]
    at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:560) [spigot-1.8.7.jar:git-Spigot-6d0ae89-a03743b]
    at java.lang.Thread.run(Thread.java:745) [?:1.8.0_45]
Caused by: java.lang.NoClassDefFoundError: org/bukkit/craftbukkit/libs/com/google/gson/GsonBuilder
    at me.botsko.prism.actions.GenericAction.<init>(GenericAction.java:34) ~[?:?]
    at me.botsko.prism.actions.BlockAction.<init>(BlockAction.java:26) ~[?:?]
    at me.botsko.prism.actions.BlockChangeAction.<init>(BlockChangeAction.java:13) ~[?:?]
    at me.botsko.prism.actionlibs.ActionFactory.createBlockChange(ActionFactory.java:87) ~[?:?]
    at me.botsko.prism.listeners.PrismBlockEvents.onBlockSpread(PrismBlockEvents.java:251) ~[?:?]
    at sun.reflect.GeneratedMethodAccessor261.invoke(Unknown Source) ~[?:?]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_45]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[?:1.8.0_45]
    at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:306) ~[spigot-1.8.7.jar:git-Spigot-6d0ae89-a03743b]
    ... 12 more