1. Create a new map
2. Put it in the crafting grid and put paper everywhere next to it more than once
3. Take the new extended map
4. Without placing it in the inventory, place it in the center again.
5. Repeat step 3 to 4 until you crash.

Crash log:

---- Minecraft Crash Report ----
// Don't do that.

Time: 18/04/13 7:08 PM
Description: Updating screen events

java.lang.NullPointerException
at wo.d(SourceFile:235)
at wm.a(SourceFile:317)
at uk.b(SourceFile:41)
at uk.a(SourceFile:58)
at tj.a(SourceFile:237)
at bds.a(SourceFile:287)
at ayl.a(SourceFile:581)
at ayl.a(SourceFile:413)
at axr.d(SourceFile:127)
at axr.m(SourceFile:111)
at net.minecraft.client.Minecraft.l(SourceFile:1078)
at net.minecraft.client.Minecraft.K(SourceFile:574)
at net.minecraft.client.Minecraft.run(SourceFile:526)
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 wo.d(SourceFile:235)
at wm.a(SourceFile:317)
at uk.b(SourceFile:41)
at uk.a(SourceFile:58)
at tj.a(SourceFile:237)
at bds.a(SourceFile:287)
at ayl.a(SourceFile:581)
at ayl.a(SourceFile:413)
at axr.d(SourceFile:127)
at axr.m(SourceFile:111)

– Affected screen –
Details:
Screen name: ayw

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [bdw['Runemoro'/703290, l='MpServer', x=-289.26, y=81.62, z=-99.47]]
Chunk stats: MultiplayerChunkCache: 49
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: World: (117,64,250), Chunk: (at 5,4,10 in 7,15; contains blocks 112,0,240 to 127,255,255), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 54821023 game time, 12530166014 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Forced entities: 5 total; [bdw['Runemoro'/703290, l='MpServer', x=-289.26, y=81.62, z=-99.47], qg['Bat'/698763, l='MpServer', x=-276.63, y=57.70, z=-116.88], bfl['haziq'/647858, l='MpServer', x=-258.97, y=75.00, z=-135.72], sf['Skeleton'/703317, l='MpServer', x=-260.23, y=54.00, z=-130.02], qg['Bat'/699975, l='MpServer', x=-301.41, y=52.00, z=-88.88]]
Retry entities: 0 total; []
Stacktrace:
at bdt.a(SourceFile:282)
at net.minecraft.client.Minecraft.b(SourceFile:1881)
at net.minecraft.client.Minecraft.run(SourceFile:535)
at java.lang.Thread.run(Unknown Source)

– System Details –
Details:
Minecraft Version: 1.5.1
Operating System: Windows 8 (x86) version 6.2
Java Version: 1.7.0_11, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 37222432 bytes (35 MB) / 94887936 bytes (90 MB) up to 1037959168 bytes (989 MB)
JVM Flags: 1 total; -Xmx1024m
AABB Pool Size: 12931 (724136 bytes; 0 MB) allocated, 2 (112 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
LWJGL: 2.4.2
OpenGL: AMD Radeon HD 6520G GL version 4.2.11931 Compatibility Profile Context, ATI Technologies Inc.
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Texture Pack: Default
Profiler Position: N/A (disabled)
Vec3 Pool Size: 56 (3136 bytes; 0 MB) allocated, 16 (896 bytes; 0 MB) used