return 400 error if pipeline not specified and no default pipeline found

Author: g-simmons

papercast/server.py

@@ -43,7 +43,10 @@ async def _add(
         elif "default" in self._pipelines.keys():
             pipeline = self._get_pipeline("default")
         else:
-            return {"message": "Pipeline not specified and no default pipeline found"}
+            raise HTTPException(
+                status_code=400,
+                detail="Pipeline not specified and no default pipeline found",
+            )
 
         loop = asyncio.get_running_loop()