CRAFTBOOK-3043 - Reported by Nabawi.Azizul

I tried to enable this by removing all configuration file, with and without other plugins, Bukkit and Spigot, tested on both 1.7.9 and 1.7.10
This worked fine on previous CraftBook version 3.8.9, Spigot 1.7.2

This same error log keep coming up

[19:11:12] [Server thread/WARN]: [CraftBook] Failed to enable mechanic: CustomDrops
java.lang.NullPointerException
at com.sk89q.craftbook.mechanics.drops.CustomDrops.load(CustomDrops.java:91) ~[craftbook-3.9-SNAPSHOT.jar:3.9-SNAPSHOT]
at com.sk89q.craftbook.mechanics.drops.CustomDrops.enable(CustomDrops.java:48) ~[craftbook-3.9-SNAPSHOT.jar:3.9-SNAPSHOT]
at com.sk89q.craftbook.bukkit.CraftBookPlugin.setupCraftBook(CraftBookPlugin.java:573) [craftbook-3.9-SNAPSHOT.jar:3.9-SNAPSHOT]
at com.sk89q.craftbook.bukkit.CraftBookPlugin.onEnable(CraftBookPlugin.java:432) [craftbook-3.9-SNAPSHOT.jar:3.9-SNAPSHOT]
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:316) [spigot.jar:git-Spigot-1595]
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:329) [spigot.jar:git-Spigot-1595]
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:405) [spigot.jar:git-Spigot-1595]
at org.bukkit.craftbukkit.v1_7_R4.CraftServer.loadPlugin(CraftServer.java:476) [spigot.jar:git-Spigot-1595]
at org.bukkit.craftbukkit.v1_7_R4.CraftServer.enablePlugins(CraftServer.java:394) [spigot.jar:git-Spigot-1595]
at net.minecraft.server.v1_7_R4.MinecraftServer.n(MinecraftServer.java:360) [spigot.jar:git-Spigot-1595]
at net.minecraft.server.v1_7_R4.MinecraftServer.g(MinecraftServer.java:334) [spigot.jar:git-Spigot-1595]
at net.minecraft.server.v1_7_R4.MinecraftServer.a(MinecraftServer.java:290) [spigot.jar:git-Spigot-1595]
at net.minecraft.server.v1_7_R4.DedicatedServer.init(DedicatedServer.java:210) [spigot.jar:git-Spigot-1595]
at net.minecraft.server.v1_7_R4.MinecraftServer.run(MinecraftServer.java:458) [spigot.jar:git-Spigot-1595]
at net.minecraft.server.v1_7_R4.ThreadServerApplication.run(SourceFile:628) [spigot.jar:git-Spigot-1595]

Comment by me4502

This was caused by the lack of rewards section in the custom drops file. The requirement for it has been removed in the current dev build.