Why am I getting this null reference error?

Question

NullReferenceException: Object reference not set to an instance of an object

ServiceAPI sp = null;
StorageService storageService = null; // Initializing Storage Service.
    

void Update(){

    storageService = sp.BuildStorageService();

    }

 

I'm getting the null reference error for the storageService = sp.BuildStorageService(); but I have it set up exactly like this in other scripts and it works fine. 

just needed sp = new ServiceAPI(*,*)