Editor crashes while selecting "Insert base" for a Prefab Variant from 'Change base in currently open Variant' pop-up window

Steps to Repro:
1. Open attached project
2. Open 'Cube Variant' Prefab Asset in Prefab Mode
3. Drag 'Cube Variant' root Prefab instance to Project Browser
4. Choose 'Insert Base' option in 'Change base in currently open Variant' confirmation dialog

Actual Result:
Editor crashes while selecting "Insert base" for a Prefab Variant from 'Change base in currently open Variant' pop-up window

Expected Result:
New 'Cube Variant Variant' Prefab Asset is created in Project Browser

Occurring with:
2019.1.0a10

For 2018.3 the issue was introduced somewhere between 2018.3.0b12 (5d10807a835e) (Reproducible) and 2018.3.0b11 (45aaf16dbe1a) (Not repro)

Working with:
2019.1.0a9, 2018.3.0b11

Environment:
Windows and Mac

Note: Bug reporter doesn't open up so the Crash Log & Project is attached manually.