When users throw items into a nether portal, the server crashes. Turning the nether off will prevent the crash:

---- Minecraft Crash Report ----
// I'm sorry, Dave.

Time: 12/28/14 10:22 PM
Description: Ticking entity

java.lang.NullPointerException: Ticking entity
at ayv.f(SourceFile:263)
at are.b(SourceFile:123)
at are.a(SourceFile:59)
at sp.a(SourceFile:514)
at wx.c(SourceFile:1749)
at adx.c(SourceFile:312)
at wx.K(SourceFile:303)
at wx.t_(SourceFile:266)
at adx.t_(SourceFile:77)
at aqr.a(SourceFile:1407)
at qu.a(SourceFile:600)
at aqr.g(SourceFile:1385)
at aqr.i(SourceFile:1278)
at qu.i(SourceFile:478)
at net.minecraft.server.MinecraftServer.A(SourceFile:608)
at pp.A(SourceFile:299)
at net.minecraft.server.MinecraftServer.z(SourceFile:532)
at net.minecraft.server.MinecraftServer.run(SourceFile:448)
at java.lang.Thread.run(Unknown Source)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– Head –
Stacktrace:
at ayv.f(SourceFile:263)
at are.b(SourceFile:123)
at are.a(SourceFile:59)
at sp.a(SourceFile:514)
at wx.c(SourceFile:1749)
at adx.c(SourceFile:312)
at wx.K(SourceFile:303)
at wx.t_(SourceFile:266)
at adx.t_(SourceFile:77)
at aqr.a(SourceFile:1407)
at qu.a(SourceFile:600)
at aqr.g(SourceFile:1385)

– Entity being ticked –
Details:
Entity Type: Item (adx)
Entity ID: 698
Entity Name: item.tile.thinGlass
Entity's Exact location: -1299.00, 71.37, 202.00
Entity's Block location: -1299.00,71.00,202.00 - World: (-1299,71,202), Chunk: (at 13,4,10 in -82,12; contains blocks -1312,0,192 to -1297,255,207), Region: (-3,0; contains chunks -96,0 to -65,31, blocks -1536,0,0 to -1025,255,511)
Entity's Momentum: 0.08, -0.29, 0.22
Entity's Rider: ~_ERROR~ NullPointerException: null
Entity's Vehicle: ~_ERROR~ NullPointerException: null
Stacktrace:
at aqr.i(SourceFile:1278)
at qu.i(SourceFile:478)

– Affected level –
Details:
Level name: AllTheWorld
All players: 1 total; [qx['Minecraftboy2019'/8, l='AllTheWorld', x=-10395.01, y=71.38, z=1618.86]]
Chunk stats: ServerChunkCache: 493 Drop: 0
Level seed: 111111111199
Level generator: ID 00 - default, ver 1. Features enabled: true
Level generator options:
Level spawn location: 228.00,64.00,-60.00 - World: (228,64,-60), Chunk: (at 4,4,4 in 14,-4; contains blocks 224,0,-64 to 239,255,-49), Region: (0,-1; contains chunks 0,-32 to 31,-1, blocks 0,0,-512 to 511,255,-1)
Level time: 175475774 game time, 3337 day time
Level dimension: 0
Level storage version: 0x04ABD - Anvil
Level weather: Rain time: 4105 (now: false), thunder time: 95001 (now: false)
Level game mode: Game mode: adventure (ID 2). Hardcore: false. Cheats: false
Stacktrace:
at net.minecraft.server.MinecraftServer.A(SourceFile:608)
at pp.A(SourceFile:299)
at net.minecraft.server.MinecraftServer.z(SourceFile:532)
at net.minecraft.server.MinecraftServer.run(SourceFile:448)
at java.lang.Thread.run(Unknown Source)

– System Details –
Details:
Minecraft Version: 1.8.1
Operating System: Windows 8.1 (amd64) version 6.3
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 1623284456 bytes (1548 MB) / 3624927232 bytes (3457 MB) up to 3817865216 bytes (3641 MB)
JVM Flags: 2 total; -Xms2048M -Xmx4096M
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
Profiler Position: N/A (disabled)
Player Count: 1 / 20; [qx['Minecraftboy2019'/8, l='AllTheWorld', x=-10395.01, y=71.38, z=1618.86]]
Is Modded: Unknown (can't tell)
Type: Dedicated Server (map_server.txt)