MetricApiController.cs

 public async Task<IActionResult> CategoryMetric(string startingDate, int? schoolId)
 {
    var currentUser = (await UserManager.FindByEmailAsync(User.Identity.Name));
    try
    {
        if (GetSchoolToSearch(currentUser, schoolId) == null && !currentUser.IsInRole("Admin"))
            return BadRequest(Localizer["UserIsNotSchoolGroupAdmin"]);
        return Ok(GetSchoolGroupAccesedResources(schoolId,
                                                  currentUser.SchoolGroup, DateTime.ParseExact(startingDate,
                                                      "dd/MM/yyyy",
                                                      CultureInfo.InvariantCulture)));
    }
    catch (NullReferenceException)
    {
        return BadRequest(Localizer["UserDoesNotBelongToASchool"]);
    }
 }