How to reproduce:
1. Open the attached project
2. Open the "Main.scene" scene
3. Drag the "Button - Write" GameObject from the Hierarchy (Canvas - Main/Container - ScreenManager/Canvas - Menu/Container - Content/Buttons - Message/Button - Write) to the Project window.
4. Select "new Prefab Variant"

Actual result: Unity crashes.

Reproducible with: 2018.3.0b12.
Not reproducible with 2019.1.0a13, 2018.3.1f1, 2018.3.0b13, 2018.3.0b11.

Note:
Can't check earlier versions because the project gets corrupted.

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Fixed in 2018.3.0b13.