NullCode.cs

  class Developer
  {
      public string FirstName { get; set; }
      public string LastName { get; set; }

      public Developer(string firstName)
      {
          FirstName = firstName;
      }
  }

  class Program
  {
      static void Main(string[] args)
      {
          var jsDev = new Developer("Dawid");
          var devInitials = GetInitials(jsDev);
      }

      static string GetInitials(Developer jsDev)
      {
          return $"{jsDev.FirstName[0]}{jsDev.LastName[0]}";
      }
  }