BRP requests without params are rejected, even for paramless methods

[splo]

Bevy version and features

• main at commit 53ddd5e615ae15ad796b36724ddd67516bec0c84.
• Relevant area: crates/bevy_remote.

What you did

I sent a BRP request over HTTP to a method that does not need any params, for example rpc.discover (other methods are affected as well), without including a params field:

curl --request POST \
  --url http://localhost:15702/ \
  --header 'content-type: application/json' \
  --data '{
  "jsonrpc": "2.0",
  "id": 0,
  "method": "rpc.discover"
}'

What went wrong

• Expected: successful response with the method result.
• Actual: error response indicating that the params field is missing:

{
  "jsonrpc": "2.0",
  "id": 0,
  "error": {
    "code": -32600,
    "message": "missing field `params`"
  }
}

This is a regression. The documentation states:

The params field may be omitted for certain methods.

Additional information

Passing params: null works:

curl --request POST \
  --url http://localhost:15702/ \
  --header 'content-type: application/json' \
  --data '{
  "jsonrpc": "2.0",
  "id": 0,
  "method": "rpc.discover",
  "params": null
}'

This is likely a result of the recent PR #23175 that introduced a custom (de)serializer for BrpRequest.

let params = params.ok_or_else(|| de::Error::missing_field("params"))?;

[kfc35]

I confirmed that omitting params in a request like world.list_components now errors a bit unexpectedly #23451
I can confirm that it’s a regression. release-0.18.1 works when params is omitted (i.e. with a request like curl -d'{"jsonrpc":"2.0","method":"world.list_components","id":1}' -X POST -H "Accept: applcation/json" -H "Content-Type: application/json" http://127.0.0.1:15702 while running the server example)