PasswordService.java

public class PasswordService
{
    private PasswordHasher passwordHasher;
    
    public PasswordService(PasswordHasher passwordHasher)
    {
        this.passwordHasher = passwordHasher;
    }
    
    void hashPassword(String password)
    {
        this.passwordHasher.hashPassword(password);
    }
}

There should be this.passwordHasher instead of hasher. Line 12

thanks @procopym