C#

public class IBase<T> where T:IBase<T>{

     public void Foo(T arg){
     }

     void Bar(){
         Foo(this); //<-- argument 1 cannot convert from  IBase<T> to T
     }
 }

 public class Deriv:IBase<Deriv>{
     void Bar2(){
         this.Foo(this); // <--- here is OK, no errors
     }
 }

var url = "https://www.marketplace.com/sh/ord/details?srn=216&orderid=" + _ebayOrder.OrderNumber;
var psi = new ProcessStartInfo()
{
    FileName = "cmd",
    WindowStyle = ProcessWindowStyle.Hidden,
    UseShellExecute = false,
    CreateNoWindow = true,
    Arguments= "/c start " + url
};
Process.Start(psi);

System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=Tweetinvi.Logic
  StackTrace:
   at Tweetinvi.Logic.JsonConverters.JsonLanguageConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)
   at Tweetinvi.Logic.JsonConverters.JsonPropertyConverterRepository.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.DeserializeConvertable(JsonConverter converter, JsonReader reader, Type objectType, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.SetPropertyValue(JsonProperty property, JsonConverter propertyConverter, JsonContainerContract containerContract, JsonProperty containerProperty, JsonReader reader, Object target)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.Serialization.JsonSerializerProxy.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonSerializer.Deserialize(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonSerializer.Deserialize[T](JsonReader reader)
   at Tweetinvi.Logic.JsonConverters.JsonInterfaceToObjectConverter`2.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.DeserializeConvertable(JsonConverter converter, JsonReader reader, Type objectType, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonSerializer.Deserialize(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonConverter[] converters)
   at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonConverter[] converters)
   at Tweetinvi.Logic.Wrapper.JsonConvertWrapper.DeserializeObject[T](String json, JsonConverter[] converters)
   at Tweetinvi.Logic.JsonConverters.JsonObjectConverter.DeserializeObject[T](String json, JsonConverter[] converters)
   at Tweetinvi.Credentials.TwitterAccessor.ExecuteGETQuery[T](String query, JsonConverter[] converters)
   at Tweetinvi.Factories.User.UserFactoryQueryExecutor.GetAuthenticatedUser(IGetAuthenticatedUserParameters parameters)
   at Tweetinvi.Factories.User.UserFactory.GetAuthenticatedUser(ITwitterCredentials credentials, IGetAuthenticatedUserParameters parameters)
   at Tweetinvi.User.GetAuthenticatedUser(ITwitterCredentials credentials, IGetAuthenticatedUserParameters parameters)
   at WindowsFormsApp1.Form1.Form1_Load(Object sender, EventArgs e) in C:\Users\kaushal dave\source\repos\ConsoleApp2\WindowsFormsApp1\Form1.cs:line 27

  This exception was originally thrown at this call stack:
    [External Code]
    WindowsFormsApp1.Form1.Form1_Load(object, System.EventArgs) in Form1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using Tweetinvi;

namespace WindowsFormsApp1
{
    public partial class Form1: Form
    {
        public Form1()
        {
            InitializeComponent();
            Auth.SetUserCredentials("gMy1b6ibNDXWxxxxxxxxxxxxxxx",
                "SegnDBtorp2FzHG2zEaF22Z9zxxxxxxxxxxxxxxxxxxxxxxxx",
                "8808475446533160xxxxxxxxxxxxxxxxxxxxxxxxxx",
                "RgFrgQJOMnJxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            var user = User.GetAuthenticatedUser();
            pbProfileImage.ImageLocation = user.ProfileBackgroundImageUrl;
            lblProfileName.Text = user.Name;
            lblProfileHendler.Text = user.ScreenName;
        }
    }
}