Unapplied import settings pop up doesnt appear on selecting Apply in the Sprite Import settings when mosaic property is unchecked while generating custom outline also exception is thrown in the console, refer attached video and .PSB file

Steps to Reproduce:
1. Create a New Project with 2D Template
2. Import .PSB file in the project.
3. Window > 2D > Sprite editor.
4. Project > Fei_Cel_group.PSB .
5. Sprite editor > Custom outline > select Sprite > Outline Tolerance(0.5) > Genrate
6. Project > Fei_Cel_group (1).psb > Insprctor > Uncheck mosaic > Apply

Actual Result:
"Unapplied import settings" doesn't prompt and Exception thrown on selecting Apply from Import settings

Expected Result:
Popup appears which asks to apply unapplied import settings

Reproducible on:
2020.2.0a10, 2020.2.0a3, 2020.1.0b8, 2020.1.0b3

Working fine on:
2020.2.0a2,2020.1.0b2

Package Found version: 4.2.2, 4.2.1, 4.1.1

Environment:
Windows 10 and macOS 10.14