- Fix a bug introduced in 1.139.1 where a client could receive an Internal Server Error if they set `device_keys: null` in the request to [`POST /_matrix/client/v3/keys/upload`](https://spec.matrix.org/v1.16/client-server-api/#post_matrixclientv3keysupload). ([\#19023](https://github.com/element-hq/synapse/issues/19023))