Using UserPrincipal in a Repository class results in null object. .Net 6

using Directory.Services.AccountManagement;
using HumanResources.JobsContext;
using HumanResources.Models;
using HumanResources.Controllers;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Microsoft.Data.SqlClient;

Public Class Repository : Controller
{

[HttpPost]
        public ActionResult PostIndexInternal(IFormFile file, Job job)
        {       
            PrincipalContext pc = new PrincipalContext(ContextType.Domain, "PPS");
            UserPrincipal up = UserPrincipal.FindByIdentity(pc, User.Identity.Name);
            string first = up.GivenName;
            string last = up.Surname;
            string full = first + " " + last;
                
                if (file != null)
                {
                    if (file.Length > 0)
                    {
                        //Get File Name
                        var fileName = Path.GetFileName(file.FileName);
                        //Get File Extension
                        var fileExtension = Path.GetExtension(fileName);
                        //Create New File Name based on AD Credentials
                        var newFileName = String.Concat(user, fileExtension);

                        //Creating new object on the database
                        var fileObject = new InternalJob()
                        {
                            IdJob = job.Id,
                            Title = job.Title,
                            EmployeeID = employeeID,
                            FileName = newFileName,
                            EmployeeName = user,
                            CurrentJobTitle = currentPosition,
                            DateApplied = DateTime.Now,
                            Active = true
                        };
                        using (var target = new MemoryStream())
                        {
                            file.CopyTo(target);
                            fileObject.FileData = target.ToArray();
                        }
                        _hrContext.InternalJobs.Add(fileObject);
                        _hrContext.SaveChanges();
                        return RedirectToAction(nameof(JobsApplied));
                    }
                }
                else if (file == null)
                {
                    string msg = "Please do not forget to select and upload the Resume";
                    return Json(msg);

                }

            return RedirectToAction(nameof(JobsApplied));
        }

}
//This would be in the HomeController
[HttpPost]
public IActionResult Example(IFormFile file, Job job)
{
    Repository repository = new Repository(_context);
    return repository.PostIndexInternal(IFormFile file, Job job);

}   

Everytime I use UserPrincipal in the Controller folder this actually works. But if I were to move the UserPrincipal in the Repository class I get the null reference error. The idea is to use a Repository class to store the code and then run a cleaner code in the controller.Any Ideas would actually help. I am stuck in this part using the UserPrincipal in the Repository class. Repository Class is located in the Models directory. Technically everything else works fine but every time I have tried doing this with userprincipal in Repository class it throws the null reference error.