When creating a Differential diff manually via /differential/diff/create/ in the web browser instead of using Arcanist, setIsCreateTransaction(true) for the transaction type DifferentialDiffTransaction::TYPE_DIFF_CREATE to avoid an empty Transaction field in the Feed and avoid strncmp() complaining about a null value being passed.
For gory details, see the comments in T15659.
ERROR 8192: strncmp(): Passing null to parameter #1 ($string1) of type string is deprecated at [/var/www/html/phorge/phorge/src/applications/policy/query/PhabricatorPolicyQuery.php:314]
Closes T15659