Emulator: emulator: ERROR: Missing initial data partition file:
As per the comment of @user4938227 (and my experience) it seems like it's a one time warning the should happen at the first run of the emulator. Avd creates the file and on the following runs it shouldn't appear.
Update
You need to update Android Emulator and HAXM,
- Go to
Tools > SDK Manager - Update Android Emulator and HAXM installer
