R1:dce6dd5d02bb

Add an explicit "null" to a missed `diffusion.branchquery` callsite to fix Diffusion "Branches" page

Summary:
See PHI775. See D19499. Originally, see PHI720.

D19499 broke the standalone "Branches" page for commits. Normally, you reach this by taking these steps:

- View a commit which is contained by 11 or more branches.
- Click the "More Branches..." link in the "Branches" field.
- You should be taken to a list of all branches which contain the commit.

The change to the 'branch' parameter was…