Steps to reproduce:
1. Open QA-supplied project ("Sample Bug.zip")
2. Select and open "New Shader Sub Graph" in the Assets folder
3. Add a Sample Texture 2D node

[2019.2.0a9]
Package Manager does not display the Shader Graph package, but it reproduces with HDRP 5.10.0,
Downgrading to 5.1.0 starts throwing "NullReferenceExceptions" and disables the ability to add a Texture 2D node in the Shader Graph
Upgrading it back up to 5.3.1 starts throwing "Cannot create required material because shader is null" error, alongside "AssertionException: Assertion failure. Value was Null". Shader Graph is not interactable.
Upgrading HDRP to 5.7.2 reproduces the issue again.
Downgrading to 5.6.1 reproduces the issue

[2019.1.0b8]
Reproduces with Shader Graph 5.6.1 in further testing by going back on the version breaks Package Manager and the Shader Graph is no longer openable.

[2018.3.10f1]
Not reproduced in Shader Graph 4.10.0

Note:
Opening project in 2018.3.10.f1 and opening it again in 2019.1.0b8 and reimporting assets seems to fix the crashing