When starting a game today in the launcher, I got the following error, and it told me to report it here. Note that I've never had this before when opening the same profile.

java.lang.NullPointerException
at net.minecraft.launcher.GameLauncher.getMinecraftArguments(GameLauncher.java:315)
at net.minecraft.launcher.GameLauncher.launchGame(GameLauncher.java:250)
at net.minecraft.launcher.GameLauncher.onDownloadJobFinished(GameLauncher.java:513)
at net.minecraft.launcher.updater.download.DownloadJob.startDownloading(DownloadJob.java:75)
at net.minecraft.launcher.Launcher$1.run(Launcher.java:157)
at java.util.concurrent.Executors$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)

Sorry if this is a dup, didn't get anything from searching. Also, I was using launcher 1.2.4 but it won't show up in "affects versions", so I put 1.2.3 instead.

When I closed and reopened the launcher the game launched 1.6.2 successfully.