problem in customizing IdentityUser ef core

Question

i want to make a relationship between aspnetusers and table uservotes.i did this relationship according to docs but whent i want to add data to uservotes and savechanges the compiler stops in savechanges line.does anyone khow the problem?thank you for any help.

   public class UserVote
{
    [Key]
    public int VoteId { get; set; }
    public string ClientId { get; set; }
    public int Hpid { get; set; }
    public int Hplid { get; set; }

    [ForeignKey(nameof(Hpid))]
    public TableHp TableHp { get; set; }
    
    [ForeignKey(nameof(Hplid))]
    public TableHpl TableHpl { get; set; }
  
    [ForeignKey(nameof(ClientId))]
    public ApplicationUser Applicationuser { get; set; }
}
public class ApplicationUser:IdentityUser
{
    public virtual List<UserVote> UserVotes { get; set; }
}
    public async Task<int> AddvoteForHp(int hpid, string userid)
    {
        UserVote vote = new UserVote()
        {
            Hpid = hpid,
            ClientId = userid
        };
        await _context.AddAsync(vote);
        await _context.SaveChangesAsync();
        var user = await GetPersonByIdAsync(hpid);
        user.Like++;
        _context.TableHps.Update(user);
        await _context.SaveChangesAsync();
    
        return user.Like;
    }