Reproduction steps:
1. Create a new Project with URP or HDRP
2. In the Project window create a new Unlit Graph and open it
3. In the Shader Graph window create a Fog Node and connect the density output with Unlit Master Node color input
4. Create a new material and assign the created shader graph
5. Apply the material to a GameObject

Expected result: Fog Node density returns 1 when connected to an Unlit Master Node
Actual result: Fog Node density returns 0 when connected to an Unlit Master Node

Reproduces on: Shader Graph 7.1.1 (2019.3.0b5), Shader Graph 7.1.8 (2019.3.0f6, 2020.1.0a22)
Does not reproduce on: Shader Graph 4.10.0-Preview (2018.4.17f1), Shader Graph 7.0.1 (2019.3.0b4)
Could not test with 2017.4 due to the package not existing

Notes:
-Does not reproduce with the PBR Master Node