java.lang.NullPointerException and end of stream

There's also another exception 2 seconds later, here's the log:

2013-05-10 23:16:15 [SEVERE] Reached end of stream
2013-05-11 09:16:59 [SEVERE] Reached end of stream
2013-05-11 09:17:05 [INFO] **** logged in with entity id 151 at (2.5511040892606154, 66.0, -25.62285088069156)
java.lang.NullPointerException
        at ek.a(SourceFile:231)
        at fh.a(SourceFile:50)
        at ek.a(SourceFile:222)
        at ck.h(SourceFile:182)
        at ck.d(SourceFile:16)
        at cm.run(SourceFile:115)
2013-05-11 09:17:05 [INFO] **** lost connection: disconnect.genericReason
2013-05-11 09:17:05 [INFO] **** lost connection: disconnect.genericReason
2013-05-11 09:17:07 [SEVERE] Reached end of stream
java.lang.IllegalArgumentException: Empty string not allowed
        at cg.<init>(SourceFile:15)
        at bu.a(SourceFile:77)
        at asc.e(SourceFile:186)
        at asc.b(SourceFile:112)
        at alj.a(SourceFile:88)
        at alj.a(SourceFile:76)
        at jb.a(SourceFile:646)
        at jb.a(SourceFile:631)
        at net.minecraft.server.MinecraftServer.a(SourceFile:265)
        at net.minecraft.server.MinecraftServer.r(SourceFile:412)
        at net.minecraft.server.MinecraftServer.run(SourceFile:341)
        at gr.run(SourceFile:584)

I encountered this problem today as well, running 13w19a. It appears to be related to the display location 'belowName' or possibly the 'health' objective in the scoreboard system. I found a similar bug (https://mojang.atlassian.net/browse/MC-15134) and they had found that deleting scoreboard.dat from the world's data folder solved the problem.
I had recently added a 'health' objective to display 'belowName'. I opened scoreboard.dat and deleted the tag 'slot_2' under display. This fixed the problem.

To reproduce in 13w19a, set health to display below a the players' name. Log out, and attempt to log in again. At this point you should receive the end of stream error.

I can also confirm that removing a 'health' scoreboard objective will fix this problem.