Editor quits when a Block from "Simple Swarm Particle System" is converted again with the same Subgraph Block, refer attached video and Stack Trace text file

Steps to repro:
1. Create a new project
2. Windows > Package Manager > Visual Effects Graph > Install
3. Project > Packages > Visual Effect Graph > Editor > Templates > Open Simple Swarm Particle System
4. Select any Block under "Simple Swarm Particle System"
5. Convert to Subgraph Block
6. Again convert the same Block to Subgraph Block

Actual Result:
Editor quit on converted again with the same Subgraph Block

Expected Result:
Block gets converted into subgraph gracefully

Reproducible in:
2020.1.0a6, 2019.3.0b4

Working fine on:
2019.3.0b3, 2019.3.0a10

Package version found: 7.1.2, 7.1.1

Package version working fine: 7.0.1, 7.0.0

NOTE:
Visual Effect Graph is introduced in 2019.3.0a10.

Environment:
Windows 10 & macOS 10.14