public bool AddSkill(short skillVNum)
        {
            Skill skillinfo = ServerManager.GetSkill(skillVNum);
            if (skillinfo == null)
            {
                Session.SendPacket(GenerateSay(Language.Instance.GetMessageFromKey("SKILL_DOES_NOT_EXIST"), 11));
                return false;
            }
            if (skillinfo.SkillVNum < 200)
            {
                if (Skills.GetAllItems()
                    .Any(s => skillinfo.CastId == s.Skill.CastId && s.Skill.SkillVNum < 200 && s.Skill.UpgradeSkill > skillinfo.UpgradeSkill))
                {
                    // Character already has a better passive skill of the same type.
                    return false;
                }
                foreach (CharacterSkill skill in Skills.GetAllItems().Where(s => skillinfo.CastId == s.Skill.CastId && s.Skill.SkillVNum < 200))
                {
                    Skills.Remove(skill.SkillVNum);
                }
            }
            else
            {
                if (Skills.ContainsKey(skillVNum))
                {
                    Session.SendPacket(GenerateSay(Language.Instance.GetMessageFromKey("SKILL_ALREADY_EXIST"), 11));
                    return false;
                }

                if (skillinfo.UpgradeSkill != 0)
                {
                    CharacterSkill oldupgrade = Skills.FirstOrDefault(s =>
                        s.Skill.UpgradeSkill == skillinfo.UpgradeSkill
                        && s.Skill.UpgradeType == skillinfo.UpgradeType && s.Skill.UpgradeSkill != 0);
                    if (oldupgrade != null)
                    {
                        Skills.Remove(oldupgrade.SkillVNum);
                    }
                }
            }
            Skills[skillVNum] = new CharacterSkill
            {
                SkillVNum = skillVNum,
                CharacterId = CharacterId
            };

            Session.SendPackets(GenerateQuicklist());
            Session.SendPacket(UserInterfaceHelper.GenerateMsg(Language.Instance.GetMessageFromKey("SKILL_LEARNED"), 0));
            return true;
        }