How do I test the return value of a function which returns an object

[SkiNLaB]

Public Sub addOrderItem(orderItem As clsOrderItem)
    If getOrderItem(orderItem.product) = nothing Then
        colOrderItems.Remove orderItem.product
    End If
    colOrderItems.Add orderItem, orderItem.product
End Sub
 
Public Function getOrderItem(product As String) As clsOrderItem
    On Error GoTo errH
    Set getOrderItem = colOrderItems(product)
    Exit Function
errH:
    Set getOrderItem = Nothing
End Function

how do i test if the getOrderItem function returns nothing (ie if the orderItem isnt in the colOrderItems collection

i figured that would work, but it says "Invalid use of object" and highlights the Nothing keyword