When register a tool with no input argument (no need to pass any args) The properties field is missing

[HChengH]

version using: v0.23.1

Error msg from openAI: ValidationException: The json schema definition at toolConfig.tools.1.toolSpec.inputSchema is invalid. Fix the following errors and try again: $.properties: null found, object expected

To reproduce simply add the following tool in ur local test mcp server

mcpServer.AddTool(
    mcp.NewTool(
	"user-name-tool",
	mcp.WithDescription("User name tool, you can get the name of the current user."),
    ),
    func(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
	return &mcp.CallToolResult{
		Content: []mcp.Content{
			mcp.TextContent{
				Type: "text",
				Text: "user name is: " + "HChengH",
			},
		},
	}, nil
    },
)

First introduced #116

[HChengH]

I'm a bit confused right now... is this 'nil Properties' intentional?