1.8-1.8.9 crashes
The JIRA page for this bug suggests that it is caused by the 'usercache.json' file being corrupted.
You can fix it by deleting the file:
Open your Minecraft launcher, and click 'Edit Profile' in the bottom left hand corner. Then, click 'Open Game Dir' in the bottom right of the window that pops up. Scroll down to find the 'usercache.json' file, and delete it. Now try opening Minecraft again.
Hope this helped :)