java.lang.NullPointerException: Initializing game

What the log looks like

java\.lang\.NullPointerException: Initializing game
Description: Initializing game\s+java\.lang\.NullPointerException: Initializing game

How to fix it

1. Read the very first 'at ...' line directly underneath 'java.lang.NullPointerException: Initializing game' (skipping any 'Not Enough Crashes' line); if it contains a mod author or mod name (such as 'dmillerw.remoteio...'), update or remove that mod.
2. If you recently changed a mod configuration file—such as disabling AE2 channels or turning off items—revert that setting or remove addon mods that depend on those disabled features.
3. If the top 'at' line starts with 'net.minecraft.' and includes 'handler$' (for example 'handler$zjo000$onOpenScreen'), scroll down to the 'Mixins in Stacktrace' section of the crash report and update or test removing the mods listed under that class.
4. If the stacktrace only shows obfuscated 'net.minecraft.class_...' lines with no mod names, split your mods folder in half and test launching repeatedly (binary search) until you isolate the exact mod triggering the startup crash.

Check your own log