[gnome-db] gda_data_model_get_value_at returns null when field is null

i'm using libgda 4.2.x from branch LIBGDA_4_2 with postgresql

i noticed that from about 2 months gda_data_model_get_value_at returns  
null (not a gvalue with null content) and error not null when the  
field's content is null

why? is it a bug?

the error message is "Unable to get value for row 0 and column 2"

thanks in advance