When opened, (It has happened twice now,) It'll give me an error something like this-

Looking for update
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma
Got reply in: 1501ms
No update found.
Reversing LZMA on C:\Users\Molly\AppData\Roaming\.minecraft\launcher.pack.lzma to C:\Users\Molly\AppData\Roaming\.minecraft\launcher.pack
Exception: java.lang.NullPointerException
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma (try 2/10)
Got reply in: 0ms
No update found.
FATAL ERROR: java.lang.NullPointerException
at javax.swing.text.WrappedPlainView$WrappedLine.update(Unknown Source)
at javax.swing.text.WrappedPlainView$WrappedLine.insertUpdate(Unknown Source)
at javax.swing.text.WrappedPlainView.insertUpdate(Unknown Source)
at javax.swing.plaf.basic.BasicTextUI$RootView.insertUpdate(Unknown Source)
at javax.swing.plaf.basic.BasicTextUI$UpdateHandler.insertUpdate(Unknown Source)
at javax.swing.text.AbstractDocument.fireInsertUpdate(Unknown Source)
at javax.swing.text.AbstractDocument.processInsertStringResult(Unknown Source)
at javax.swing.text.AbstractDocument.insertString(Unknown Source)
at javax.swing.text.PlainDocument.insertString(Unknown Source)
at net.minecraft.bootstrap.Bootstrap.print(Bootstrap.java:221)
at net.minecraft.bootstrap.Bootstrap.println(Bootstrap.java:207)
at net.minecraft.bootstrap.Bootstrap.unpack(Bootstrap.java:132)
at net.minecraft.bootstrap.Bootstrap.execute(Bootstrap.java:123)
at net.minecraft.bootstrap.Bootstrap.main(Bootstrap.java:381)

Please fix the error and restart.