Fails with:
File "/nix/store/…-nix-update-1.0.0/…/nix_update/update.py", line 344, in update
update_hash = update_version(
^^^^^^^^^^^^^^^
File "/nix/store/…-nix-update-1.0.0/…/nix_update/update.py", line 318, in update_version
return replace_version(package)
^^^^^^^^^^^^^^^^^^^^^^^^
File "/nix/store/…-nix-update-1.0.0/…/nix_update/update.py", line 39, in replace_version
line = line.replace(package.rev, package.new_version.rev)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: replace() argument 1 must be str, not None
