Add Screen to Panel does not work

Hi all.

I am trying to add the Web Picker Opportunity to this screen.My page returns Object Reference not set to an instance of an object. The one in bold returns the error :

public override void BuildContents()

AddInfo($"My Company ID id : {_sCompanyId}");
//Only add the screen if there is No company in context:
if (string.IsNullOrWhiteSpace(_sCompanyId) || _sCompanyId == "0")
//Create a pannel to hold the block
HorizontalPanel webPickerPannel = new HorizontalPanel();
webPickerPannel.AddAttribute("width", "100%");
//Get The screen:
EntryGroup webPickerScreen = new EntryGroup("OpportunityWebPicker");
webPickerScreen.AddAttribute("width", "100%");
AddError("Picking up" + webPickerPannel);
//Add the screen to the pannel: