If you do something like this:
// Missing $user->getPHID()! $object->setUserPHID($user)->save();
...you get a very unhelpful exception:
Expected a scalar or null for %s conversion. Query: %s
This doesn't give you any hints about what's wrong. Instead, provide a more useful exception:
Unable to insert or update object of class DifferentialRevision, field 'title' has a nonscalar value.