Fix a regression in Subversion diff parsing.
Review Request #11724 — Created July 15, 2021 and submitted
A recent change intended to fix a deleted files indicator in Subversion
diffs regressed some parsing. We weren't checking whether the field in
None. This actually impacted a unit test, but it seems we
missed it (as CI is temporarily busted).
This change adds the necessary bullet-proofing, fixing the test.
Applicable unit tests pass.
Tested with a customer.