Object reference not set as an instance of an object

Hi when using the code bellow I get an error saying "Object reference not set as an instance of an object"
In the editor the public GameObject is set and it has the component I want to acess, I can even modify the contents of the component, however when I try to add it to the Dictionary I get the error. Am I missing something?

Code (CSharp):

1.         public SortedDictionary<int, UnitData> SelectableUnits;
2.         public GameObject unit;
3.         currentID = 1;
4.         Debug.Log(currentID);
5.         UnitData UD = unit.GetComponent<UnitData>();
6.         SelectableUnits.Add(currentID++, UD);
7.         Debug.Log(currentID);

 

You have not initialized your dictionary.

 

Thanks a ton

 

1. public SortedDictionary<int, UnitData> SelectableUnits = new SortedDIctionary<>();