Operating system: Windows-10-10.0.17763 64 Bits
Graphics card: GeForce GTX 1050 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 417.35
Broken: version: 2.80 (sub 74), branch: blender2.7, commit date: 2019-06-12 18:00, hash: rB2404220e80a9
Worked: 22.80 (sub 74) 2019-06-01 22:51, 079c7f918c81
Short description of error
Volumetric emission no longer works if density of the reflective volume is set to zero, but it works if density is greater than zero.
Exact steps for others to reproduce the error
Add a cube.
Add a shader Principled Volume and link into the Volume of the Output node
Set Density to zero in the Principled Volume
Increase Emission Strength in Principled Volume
Nothing will show.
Now increase Density to 0.1 and emission will start to shine!
But the reflective volume material will also show in this case, which is a problem if one wants to apply a texture pattern to the emission volume, e.g make a glowing sphere with a gradient node or patterns with holes etc.