Minecraft won't start

java.lang.NullPointerException
at net.minecraft.launcher.game.MinecraftGameRunner.getAssetObject(MinecraftGameRunner.java:232) ~[launcher.jar:?]
at net.minecraft.launcher.game.MinecraftGameRunner.launchGame(MinecraftGameRunner.java:146) ~[launcher.jar:?]
at com.mojang.launcher.game.runner.AbstractGameRunner.onDownloadJobFinished(AbstractGameRunner.java:177) [launcher.jar:?]
at com.mojang.launcher.updater.download.DownloadJob.popAndDownload(DownloadJob.java:122) [launcher.jar:?]
at com.mojang.launcher.updater.download.DownloadJob.access$000(DownloadJob.java:12) [launcher.jar:?]
at com.mojang.launcher.updater.download.DownloadJob$1.run(DownloadJob.java:86) [launcher.jar:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:439) [?:1.6.0_65]
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) [?:1.6.0_65]
at java.util.concurrent.FutureTask.run(FutureTask.java:138) [?:1.6.0_65]
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895) [?:1.6.0_65]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918) [?:1.6.0_65]
at java.lang.Thread.run(Thread.java:695) [?:1.6.0_65]