added from clause to save JsonDecodeError exception tiangolo#3993

fastapi/routing.py

@@ -208,7 +208,7 @@ async def app(request: Request) -> Response:
                         else:
                             body = body_bytes
         except json.JSONDecodeError as e:
-            raise RequestValidationError([ErrorWrapper(e, ("body", e.pos))], body=e.doc)
+            raise RequestValidationError([ErrorWrapper(e, ("body", e.pos))], body=e.doc) from e
         except Exception as e:
             raise HTTPException(
                 status_code=400, detail="There was an error parsing the body"