problem with calling another event

I have a DropDownList Selected Index Change event as follows, I would like to run the event when the page_load, so I write a line of code : ddlFaceList_SelectedIndexChanged(Me, e) . However, it prompts me an error like "Object reference not set to an instrance of an object".  What is wrong with my code?
 
Protected Sub ddlFaceList_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlFaceList.SelectedIndexChanged
End Sub
 
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