Instead Of Insert - Identity Null Error

I'm atempting to use an Instead of Insert Trigger on a view to insert a record into a base table. The base table boundaryline has an identity primary key defined. The following is the error I'm receiving:

The column 'id1' in table 'dbo.ParcelBoundaries1' cannot be null.
Could not insert a record in the database.

The view is as follows:

SELECT IS_TAXLOT, IS_OTHER, IS_CARTOGRAPHIC, IS_RAILROAD_ROW, IS_IRRIGATION_ROW, IS_STREET_ROW, IS_CLOSING_ROW, IS_CONSTRUCTION,
IS_CONFLICT, TYPE, GMPID, BEARING, DISTANCE_LEGAL, DISTANCE_CALCULATED, GEOMETRY, GEOMETRY_XLO, GEOMETRY_XHI,
GEOMETRY_YLO, GEOMETRY_YHI, id1
FROM dbo.BoundaryLine


The trigger is as follows:

CREATE TRIGGER TR_ParcelBoundaries1 on ParcelBoundaries1
INSTEAD OF INSERT
as

BEGIN

INSERT INTO BoundaryLine
(IS_TAXLOT,
IS_OTHER,
IS_CARTOGRAPHIC,
IS_RAILROAD_ROW,
IS_IRRIGATION_ROW,
IS_STREET_ROW,
IS_CLOSING_ROW,
IS_CONSTRUCTION,
IS_CONFLICT,
GMPID,
BEARING,
DISTANCE_LEGAL,
DISTANCE_CALCULATED,
GEOMETRY,
GEOMETRY_XLO,
GEOMETRY_XHI,
GEOMETRY_YLO,
GEOMETRY_YHI)
Select 'YES', 'NO','NO','NO','NO','NO','NO','NO','NO', GMPID, BEARING, DISTANCE_LEGAL,
DISTANCE_CALCULATED, GEOMETRY, GEOMETRY_XLO, GEOMETRY_XHI,
GEOMETRY_YLO, GEOMETRY_YHI
from
inserted

END

Any thoughts would be greatly appreciated?