The Polygong must contain the internal ring?

[lee light]

I can run the following code to create a polygon with one internal ring.
CREATE TABLE geom (g GEOMETRY);

SET @g = 'POLYGON((0 0,10 0,10 10,0 10,0 0),(5 5,7 5,7 7,5 7, 5 5))';

INSERT INTO geom VALUES (GeomFromText(@g));

But, if I want to create only one polygon without any internal ring, it failed:
SET @g = 'POLYGON(0 0,10 0,10 10,0 10,0 0)';
INSERT INTO geom VALUES (GeomFromText(@g));

I met such error:
MySQL said:

#1416 - Cannot get geometry object from data you send to the GEOMETRY field

How could I create a polygon without internal ring? I dont use linestring because the polygon will be filled with color later.
Thank you for your replay!