using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var node = "Root";

        var attrs = new Dictionary<string, string>

        {

            {"foo", "bar"},

            {"baz", null},  

        };

        var result = XpathQueryBuilder(node, attrs);

        Console.WriteLine(result);

    }

    private static string XpathQueryBuilder(string NodeName, Dictionary<string,string> attributes = null)

    {

        string XpathAttr = "";

        if (attributes != null)

        {

            XpathAttr = "[" + 

                String.Join(" and ", attributes.Select(o => 

                                 {

                                    var attrVal = o.Value ?? "*";

                                    return "@" + o.Key + "='" + attrVal + "'";

                                 })) +

                "]";

        }

        return "//" + NodeName + XpathAttr;

    }    

}