VB.net Excel AddIn System.NullReferenceException

Hi. I am using the following code when trying to log into Xero in my Excel Add-in and getting the error below.
This might be because there are two companies

    _xero.Companies.ForEach(Sub(x)
                                    Dim item = Globals.Factory.GetRibbonFactory().CreateRibbonDropDownItem()
                                    item.Label = x.TenantName
                                    item.Tag = x.TenantId.ToString
                                    cbCompanies.Items.Add(item)
                                End Sub)

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