[MC-22104] "/scoreboard teams join" does no error checking, causing a NPE

How to reproduce:

Join a nonexistent player to an existing team. E.g.: /scoreboard teams join nonexistent myteam
Join an existing player to a nonexistent team. E.g.: /scoreboard teams join player nonexistent
Join a nonexistent player to a nonexistent team. E.g.: /scoreboard teams join nonexistent nonexistent

Excepted result:
An error message telling you that the specified player/team does not exist.

Actual result:

2013-07-04 20:05:31 [INFO] An unknown error occurred while attempting to perform this command
java.lang.NullPointerException
        at atc.a(SourceFile:186)
        at hm.a(SourceFile:67)
        at ih.g(SourceFile:346)
        at ih.b(SourceFile:134)
        at aa.a(SourceFile:54)
        at ip.ar(SourceFile:295)
        at ip.t(SourceFile:263)
        at net.minecraft.server.MinecraftServer.s(SourceFile:405)
        at net.minecraft.server.MinecraftServer.run(SourceFile:339)
        at hf.run(SourceFile:582)