Getting NullReferenceException on IActionResult GetAll() in CoverTypeController.cs

[theahmadchand]

#region API CALLS
        [HttpGet]
        public IActionResult GetAll()
        {
            var allObj = _unitOfWork.SP_Call.List<CoverType>(SD.Proc_CoverType_GetAll, null); <===[System.NullReferenceException:'Object reference not set to an instance of an object.'
]
            return Json(new { data = allObj });
        }
`