After moving a level into a folder and fixing the redirectors (right click in content browser) the project will package a Null reference without throwing an error. This will let you create a project that can't opent the Game Default Level.
Found in 4.24.2 CL#11100242
Reproduced in 4.23.1 CL#9631420, 4.26 Main CL#11574810
1. Create a blank project.
2. Save two levels (Main and Other).
3. In Project Settings set the "Editor Startup Map" and "Game Default Map" to Main.
4. Create a folder and put Main in it.
5. Fix the redirectors in the folder.
6. Package the project and open it.
Result: An error is thrown "The map specified on the commandline 'Game/Main/' could not be found. Exiting."
Expected: The Main level opens as expected or an error should be thrown during packaging.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-89428 in the post.