Steps to reproduce:
1. open User's attached project with Unity 5.5.0b4 or newer

Result: an error appears: Fatal Error! GetManagerFromContext: pointer to object of manager 'GraphicsSettings' is NULL (table index 6). Project cannot be imported
Exported behavior: old project settings should be allowed to be imported in the current versions

Reproduced with: 5.5.0b5, 5.5.0b4
Not reproduced with: 5.5.0b3, 5.4.1p1, 5.3.6p5

Workaround: deleting ProjectSettings/GraphicsSettings.asset solves the issue

Note:
project can be opened without errors with 5.5.0b3 or older