Improve retrieval of most recent commit

- Use of rev-parse more correct since `git log` is
  porcelain

1 files changed, 5 insertions, 2 deletions

diff --git a/lorry.raw-file-importer b/lorry.raw-file-importer
index 1203e20..0a63003 100755
--- a/lorry.raw-file-importer
+++ b/lorry.raw-file-importer
@@ -86,10 +86,13 @@ def commit_lfs_file(raw_file, relative_path, last_commit, fast_import):
 
 def get_last_commit():
     # show the full hash of the latest commit
-    out = subprocess.run(['git', 'log', '-n1', '--format=format:%H'], capture_output=True, text=True)
+    out = subprocess.run(['git', 'rev-parse', 'HEAD'], capture_output=True, text=True)
     if out.returncode != 0:
         return None
-    return out.stdout.strip()
+
+    # Will be HEAD when no commits exist yet
+    out = out.stdout.strip()
+    return None if out == 'HEAD' else out
 
 
 def main():