If you `git commit --signoff --amend` a commit before landing, a `Signed-off-by`-line is added to the end of the commit message similar to
https://phabricator.haskell.org/rGHC40b1ee4043fefdd19ff6614a63939002840c6d97
However, this seems to confuse Differential as it didn't associated the commit with the code-rev (it usually does so, if a `Differential Revision: ...` line is contained in the commit message).