[NOTICKET][doc] add guard if filename None

src/pipeline/document_pipeline/document_pipeline.py

@@ -22,6 +22,8 @@ class DocumentPipeline:
     async def upload(self, file: UploadFile, user_id: str, db: AsyncSession) -> dict:
         """Validate → upload to blob → save to DB."""
         content = await file.read()
+        if not file.filename:
+            raise HTTPException(status_code=400, detail="Filename is required.")
         file_type = file.filename.split(".")[-1].lower() if "." in file.filename else "txt"
 
         if len(content) > MAX_FILE_SIZE_BYTES: