LSP Error response from Client is not standard conform

I have been trying my [lsp_server](https://crates.io/crates/lsp-server) language server with Qt Creator recently and I noticed that it errors out after a while

This is the last message that Creator logged as having sent:

18:55:57.863 Client
{
    "error": {
        "code": -32601
    },
    "id": 0,
    "jsonrpc": "2.0"
}

Looking into the LSP specification, an `error` part of the reply should look like this:

interface ResponseError {
    /**
    * A number indicating the error type that occurred.
    */
    code: integer;

    /**
    * A string providing a short description of the error.
    */
    message: string;

    /**
    * A primitive or structured value that contains additional
    * information about the error. Can be omitted.
    */
    data?: string | number | boolean | array | object | null;
}

I would expect Creator to send an message along with the error code.

Sorry, I do not have a newer version of creator handy, but I checked Jira and did only find a similar report about haskel LSP not accepting an completely empty error reply (which was fixed).

It would be cool if somebody could look into this: I am building on the standard library for LSPs in rust and expect them all to have similar problems as the Error bubbles up from the function reading stdio in that library.