Error: Could not find or load main class net.minecraft.client.main.Main

02:31:01.867
launcher
main
Preparing to launch minecraft client for 1.12
02:31:02.096
launcher
main
Checking installations.
02:31:02.098
launcher
main
Minecraft client 1.12 is ready to start.
02:31:02.098
launcher
main
Starting!
02:31:02.471
launcher
main
Using default game log configuration client-1.12.xml (outputs XML)
02:31:02.728
launcher
main
Error: Could not find or load main class net.minecraft.client.main.Main
02:31:02.728
monitor
Process Monitor
Process crashed with exit code 1