Upstreaming from https://phabricator.wikimedia.org/T274559; this is also the third stacktrace listed in https://secure.phabricator.com/T13667.
For random reasons out of scope for this task, imports of commits in Diffusion can get stuck, displaying Still Importing... This commit is still importing. Changes will be visible once the import finishes. That's why Phorge documentation for troubleshooting exists.
When using the "Skip past this commit" button in the leftmost column viewing a file in Diffusion to access the past of such a non-imported commit, Phabricator throws a RuntimeException: reset() expects parameter 1 to be array, null given.
Code handling should be more robust and not expose a raw RuntimeException to the user but handle the situation more gracefully.