chore: improve logging for "not a git repository" (#7944)

openhands/server/routes/files.py

@@ -202,6 +202,11 @@ async def git_changes(request: Request, conversation_id: str):
 
     try:
         changes = await call_sync_from_async(runtime.get_git_changes, cwd)
+        if changes is None:
+            return JSONResponse(
+                status_code=500,
+                content={'error': 'Not a git repository'},
+            )
         return changes
     except AgentRuntimeUnavailableError as e:
         logger.error(f'Runtime unavailable: {e}')