Blackboard window is missing in the shader graph

Steps to repro:
1. Create a new project.
2. Windows > Package Manager > Shader Graph.
3. Click on Install.
4. Right click on Project Window > Create > Shader.
5. Select PBR Graph > Double click on newly created Shader Graph.

Actual Result:
Blackboard window is missing.

Expected result:
Blackboard window is present in the Shader Graph.

Reproducible in:
2019.1.0a13, 2019.1.0a11.

Working Fine in:
2019.1.0a10, 2018.3.0f2(49866f0a5d12)

Environment:
Windows & Mac.