Fatal Error Launching Game

Put the summary of the bug you're having here

*What I expected to happen was My Minecraft is supposed to open

*What actually happened was. it say this error at net.minecraft.launcher.GameLauncher.getMinecraftArguments(GameLauncher.java:480)
at net.minecraft.launcher.GameLauncher.launchGame(GameLauncher.java:423)
at net.minecraft.launcher.GameLauncher.onDownloadJobFinished(GameLauncher.java:693)
at net.minecraft.launcher.updater.download.DownloadJob.popAndDownload(DownloadJob.java:124)
at net.minecraft.launcher.updater.download.DownloadJob.access$000(DownloadJob.java:15)
at net.minecraft.launcher.updater.download.DownloadJob$1.run(DownloadJob.java:94)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...