How to reproduce:
1. Open user's attached project
2. In the Project view navigate to Assets -> Id1 -> maps
3. Try reimporting any file

Expected result: File will be imported
Actual result: Console prints out two errors (both mentioned in notes below)

Reproducible with: 2017.1.4p2, 2017.2.3p2, 2017.4.7f1, 2018.1.9f1, 2018.2.0f2, 2018.3.0a5

Notes:
- Errors printed by console:
* Assertion failed on expression: 'm_ScriptCache != NULL && m_ScriptCache->klass'
* NullReferenceException: Object reference not set to an instance of an object
- None of the imported instances has their dedicated script attached