file.CopyTo(stream) is giving NullReferenceException, how to use Memory stream?

Question

I am trying to convert excel to a list of the model class objects in the .net core framework. But ended up getting NullReferenceException.

        public List<UserDataObject> Insert(IFormFile file)
        {
            var list = new List<UserDataObject>();
            using(var stream = new MemoryStream())
            {
                file.CopyTo(stream);
                using(var package = new ExcelPackage(stream))
                {
                    ExcelWorksheet workSheet = package.Workbook.Worksheets[0];
                    var rowCount = workSheet.Dimension.Rows;
                    for(int row = 1; row <= rowCount; row++)
                    {
                        list.Add(new UserDataObject
                        {
                            UserName = workSheet.Cells[row, 1].Value.ToString().Trim(),
                            Gender = workSheet.Cells[row, 2].Value.ToString().Trim(),
                            EmailId = workSheet.Cells[row, 3].Value.ToString().Trim(),
                            Address = workSheet.Cells[row, 4].Value.ToString().Trim(),
                            MobileNo = workSheet.Cells[row, 5].Value.ToString().Trim(),
                            PinCode = workSheet.Cells[row, 6].Value.ToString().Trim()
                    });
                    }
                }
            }
            return list;
        }

Any help?