fix: normalize nullable pull request authors (#56)

src/main.py

@@ -94,7 +94,7 @@ async def context() -> JSONResponse:
         if isinstance(i, dict)
     ]
     pr_models = [
-        PullRequest(id=p["id"], number=p["number"], title=p["title"], state=p["state"], user=p.get("user", {}).get("login", ""), url=p["html_url"])
+        PullRequest(id=p["id"], number=p["number"], title=p["title"], state=p["state"], user=(p.get("user") or {}).get("login", ""), url=p["html_url"])
         for p in prs_data[:50]
         if isinstance(p, dict)
     ]