Passing a malformed body throws a 500 error instead of 400. Very hard to figure out what is incorrect in the request being issued by the caller

Description
When sending an InitializeRequest to the MCP C# SDK server with a malformed or incomplete request body (e.g., missing required fields like clientInfo.Version, the server responds with a 500 Internal Server Error.
This behavior is problematic because:

• A 500 error implies a server-side failure, not a client-side input issue.
• According to MCP protocol expectations, the server should return a 400 Bad Request or a structured JSON-RPC error response indicating what was wrong with the request.

Steps to reproduce the behavior:

1. Issue a POST mcp call with this request body:

{ "jsonrpc": "2.0", "id": "7", "method": "initialize", "params": { "protocolVersion": "2025-06-18", "clientInfo": { "name": "Insomnia" } } }

Expected behavior
A 400 error should be returned telling the user that the ClientInfo.Version property is missing

Additional Context
Our controllers are mapped like this in our Startup.cs file:

app.UseEndpoints(endpoints => { endpoints.MapControllers(); endpoints.MapMcp("/mcp/environments/{environmentId}/servers/{serverName}"); });
and controller is defined like this:

[HttpGet] [HttpPost] [HttpDelete] [Route("mcp/environments/{environmentId}/servers/{serverName}")] public IActionResult Invoke() { return this.Ok(); }

Start at the MapMcp("/mcp/environments/{environmentId}/servers/{serverName}") endpoint mapping shown in Startup.cs and the controller's Invoke action. Reproduce the POST with the incomplete InitializeRequest, then trace request validation and error handling to determine where the 500 is produced. Done means the missing ClientInfo.Version is reported through a 400 response or structured JSON-RPC error.