Update github_rest_api/github.py

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: dclong

github_rest_api/github.py

@@ -810,7 +810,10 @@ def _head_commit_date(self, sha: str) -> str:
         ).json()
         if not isinstance(commits, list) or not commits:
             raise ValueError(f"No commits found for SHA {sha}")
-        return commits[0]["commit"]["committer"]["date"]
+        try:
+            return commits[0]["commit"]["committer"]["date"]
+        except (KeyError, TypeError) as e:
+            raise ValueError(f"Unexpected commit payload structure for SHA {sha}") from e
 
     def get_branches(self, n: int = 0) -> list[dict[str, Any]]:
         """List branches in this repository."""