Returns the outer ring of a simple area geometry. For a complex geometry with more than one outer ring, a complex line is returned containing all of the outer rings.
Parameter 1 - a simple or complex area geometry.
Returns: the outer ring geometry if there is only one, or a complex geometry containing all of the outer rings. Returns null if parameter 1 is a geometry but not an area.
If parameter 1 is not a geometry, an exception will be thrown.