KeysUploadRequest generates malformed bodies

[richvdh]

The body of KeysUploadRequest structs looks like this:

{"device_keys":null,"fallback_keys":{},"one_time_keys":{"signed_curve25519:AAAAAAAAAGY":{"key":"WEvbLtVJzuDZQTlzCowFdzfqyfjh4d8NhhyciQ4GxSs","signatures":{"@richvdh:sw1v.org":{"ed25519:JAVDMNZYHJ":"6hrLwCj+99R5lciirbmbdh2d+LbGEQEnAtv+HkEGAW1ODCa+7WDxFyoEZf74u9eWGCjSAmhd/OT5EMQ5yhWoAA"}}}}}

null is not a valid value for device_keys according to the spec, which requires it to be a JSON object if it is present.

Related: #56

[richvdh]

As with #56, this feels like a result of doing our own serialisation rather than taking advantage of the existing serialisation attributes on the underlying Ruma type. /cc @Hywan

[uhoreg]

This was fixed by #72 Can someone close this? I don't have permissions.