[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: java.lang.NullPointerException
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.darkhax.bookshelf.serialization.BlockIngredientSerializer.read(BlockIngredientSerializer.java:24)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.darkhax.bookshelf.serialization.BlockIngredientSerializer.read(BlockIngredientSerializer.java:11)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.darkhax.bookshelf.Bookshelf.onClick(Bookshelf.java:114)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:247)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraftforge.eventbus.EventBus.lambda$addListener$11(EventBus.java:239)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraftforge.eventbus.EventBus.post(EventBus.java:297)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraftforge.common.ForgeHooks.onRightClickBlock(ForgeHooks.java:789)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.server.management.PlayerInteractionManager.func_219441_a(PlayerInteractionManager.java:318)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.network.play.ServerPlayNetHandler.func_184337_a(ServerPlayNetHandler.java:958)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.network.play.client.CPlayerTryUseItemOnBlockPacket.func_148833_a(SourceFile:36)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.network.play.client.CPlayerTryUseItemOnBlockPacket.func_148833_a(SourceFile:10)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.network.PacketThreadUtil.func_225383_a(SourceFile:21)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.util.concurrent.TickDelayedTask.run(SourceFile:18)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(SourceFile:144)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.util.concurrent.RecursiveEventLoop.func_213166_h(SourceFile:23)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:733)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:159)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(SourceFile:118)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.server.MinecraftServer.func_213205_aW(MinecraftServer.java:716)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.server.MinecraftServer.func_213168_p(MinecraftServer.java:710)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213160_bf(SourceFile:103)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.server.MinecraftServer.func_213202_o(MinecraftServer.java:695)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:645)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at net.minecraft.server.MinecraftServer.lambda$startServer$0(MinecraftServer.java:232)
[10:13:18] [Server thread/INFO] [STDERR/]: [net.darkhax.bookshelf.Bookshelf:onClick:121]: at java.lang.Thread.run(Unknown Source)

I'm testing with .15 build now, hopefully it's resolved, and if so sorry for the post without latest version.

Not seeing it in .15 build, but not 100% what I was clicking on that caused it previously so I'll leave it up to you to close or not.

Thanks for resolving, this issue was fixed shortly before you opened this issue. #153