Minecraft crashes while loading snapshot

I keep getting a crash report, which I can paste under this, whenever I want to load up 17w50a.

The game crashed whilst initializing game
The game crashed whilst initializing game
Error: com.google.gson.JsonSyntaxException: com.google.gson.stream.MalformedJsonException: Invalid escape sequence at line 4 column 122 path $.pack.description
That's the crash report above.