Here is exactly what the launcher said:
[13:28:05 FATAL]: Fatal error launching game. Report this to http://mojang.atlassian.net please!
java.lang.NullPointerException
at net.minecraft.launcher.GameLauncher.getMinecraftArguments(GameLauncher.java:382) ~[launcher.jar:?]
at net.minecraft.launcher.GameLauncher.launchGame(GameLauncher.java:283) ~[launcher.jar:?]
at net.minecraft.launcher.GameLauncher.onDownloadJobFinished(GameLauncher.java:629) [launcher.jar:?]
at net.minecraft.launcher.updater.download.DownloadJob.popAndDownload(DownloadJob.java:120) [launcher.jar:?]
at net.minecraft.launcher.updater.download.DownloadJob.access$000(DownloadJob.java:12) [launcher.jar:?]
at net.minecraft.launcher.updater.download.DownloadJob$1.run(DownloadJob.java:89) [launcher.jar:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.7.0_51]
at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.7.0_51]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [?:1.7.0_51]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [?:1.7.0_51]
at java.lang.Thread.run(Unknown Source) [?:1.7.0_51]
Please fix it!
Duplicate of MCL-450 – If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.