Issue while creating a new user using Asp.net core identity

I am stuck with an issue where i am unable to create a New User using as.net core identity and i am using core 3.1. When ever i try to execute the code i get this error :

"An unhandled exception has occurred while executing the request. System.IndexOutOfRangeException: Index was outside the bounds of the array."

I am not able to understand. please find my code :

        private readonly UserManager<ApplicationUser> _userManager;
        private readonly RoleManager<IdentityRole> _roleManager;
        private readonly IApplicationDbContext _context;

        public IdentityService(UserManager<ApplicationUser> userManager, RoleManager<IdentityRole> 
        roleManager, IApplicationDbContext context)
        {
            _userManager = userManager;
            _roleManager = roleManager;
            _context = context;
        }

 var user = new ApplicationUser
            {
                FirstName = firstName,
                LastName = lastName,
                UserName = userName,
                Email = emailId
            };

            try
            {
                var result = await _userManager.CreateAsync(user, password); // here my code breaks                
            }
            catch (Exception ex)
            {
                throw ex;
            }