How to reproduce:
1. Create a new HDRP project
2. Create a new vfx graph and open it
3. Delete Output Context
4. Create Output Context
5. Link Output Context to Update
6. Save changes
7. Observe vfx asset file size or save it to text file
8. Repeat steps again from the 3rd step

Expected result: vfx asset file size remains the same there is not additional lines added to the vfx asset file (when comparing in diff tool)
Actual result: vfx asset file size increases, additional data is added to the vfx asset on each iteration(when comparing in diff tool)

Reproduced with: 2021.2.0a10(12.0.0)