I have a Dictionary declared like:

public var PoolDict : Dictionary.<String, List.<GameObject[]> >;

I made a function to add items to the list and array

function Add(key:String, obj:GameObject)
{
    if(!PoolDict.ContainsKey(key))
    {
        PoolDict[key] = new List.<GameObject[]>();
    }

    //PlaceHolder - Not what will be in final version
    PoolDict[key].Add(null);

   //Attempts - Errors- How to add to existing array?
   PoolDict[key].Add(obj);
   PoolDict[key][0].Add(obj);

}

I'd like to replace the line after //PlaceHolder with code that will assign a gameObject to an existing array in a list that's associated with a key. How could this be done?