Phabricator: error on diffs with added files

Created by: lguychard

• Point the Sourcegraph integration on phabricator.sgdev.org to umami.sgdev.org
• Visit https://phabricator.sgdev.org/D4
• Witness no code intelligence
• Witness error in console: Uncaught AggregateError: graphql: got null for non-null
• AFAICT this stems from a ResolveStagingRev request with a null baseRev:

"variables": {"repoName":"gitolite.sgdev.org/13k/facebook/react","diffID":8,"baseRev":null,"date":"1560944517","description":null,"patch":"..."}}