Response message due to Parse Error has invalid id

[emicklei]

When a MCP server is misbehaving (typically during development) and there are issues with message processing or response writing,
an Error response is written, see

mcp-go/server/stdio.go

Line 233 in edda393

response := createErrorResponse(nil, mcp.PARSE_ERROR, "Parse error")

(v0.23.0)

The createErrorResponse is called with a nil for id which is invalid according to the specification ; this causes errors in the client (when that is validating the message) and therefore hides the actual cause.

[emicklei]

According to https://modelcontextprotocol.io/docs/concepts/transports the id is either a number or string, maybe better to pass an empty string here.

[emicklei]

however, the json rpc2 spec says null is allowed:
https://www.jsonrpc.org/specification#request_object

so maybe this issue is obsolete and it is the client not handling it correctly.