Burgzerg arcade error with vital mods

Hi, I was following the burgzerg arcade tutorials fine since I know a bit about c# and I was able to solve all the issues, I typed the SetupVitalModifiers and no errors appeared at the console, but when I start the scene a Null Reference error appeared, don't know why this happens since I'm using the right variable. I'll paste the code here.

     private void SetupVitalModifiers(){
         //health
     
         GetVital ((int)VitalName.Health).AddModifier (new ModifyingAttribute (GetPrimaryAttribute ((int)AttributeName.Constitution), .5f));
 
         //mana
         ModifyingAttribute manaMod = new ModifyingAttribute ();
         manaMod.attribute = GetPrimaryAttribute ((int)AttributeName.Intellect);
         manaMod.ratio = 1;
         GetVital ((int)VitalName.Mana).AddModifier (manaMod); // AddModifier (manaMod) gives error
         
     }

And I also have a minor issue that I can not understand, my skills and vitals increase by the number of skills//vitals in my lists, I mean, say that I have 9 skills, so with ratio of 1 the skill will increase by 9 points, and if I put the ratio to 0.1f, I will need 9 points to get 9 skill points but if I have 8 points of the attribute, the skill will have 0.

I suppose that the number of vitals//skills increases the AdjustedBaseValue somehow but I can't seem to find where I made the mistake, I've seen he vids 2 more times since the error but all seems to be just fine.

I've been trying to fix these errors for 2 days, looking forward somebody knows how to fix them.

Thx for the help.

EDIT : When I add a second skill modifier happens as well, might be a problem with the AddModifier list??

 private List<ModifyingAttribute> _mods; // A list of Attributes that modfy this stat
     private int _modValue;    //ammount added to the baseValue from the modifiers
 
     public ModifiedStat(){
         _mods = new List<ModifyingAttribute> (2);
         _modValue = 0;
     }
     public void AddModifier (ModifyingAttribute mod){
         _mods.Add (mod);
     }
 
     private void CalculateModValue(){
         _modValue = 0;
 
         if (_mods.Count > 0)
             foreach(ModifyingAttribute att in _mods)
                 _modValue += (int)(att.attribute.AdjustedBaseValue * att.ratio);
     }