Rejecting Insert rows with Entity Framework and PostgreSQL

I use PostgreSQL and EF6 in some project.

I want to reject silently some rows I insert who have duplicated data. The table is very simple, looking like :

CREATE TABLE data
(
  table_id PRIMARY KEY
  table_element 
)

With id_table as a autoincrement key.

In the PostgreSQL side, I use this simple trigger to reject duplicates :

CREATE OR REPLACE FUNCTION checkDuplicate()
  RETURNS trigger AS

DECLARE
    datacount integer;
BEGIN 

 SELECT Count(table_id) into datacount 
 FROM data WHERE table_element = NEW.table_element;

IF (datacount > 0) THEN
     RETURN null;
ELSE
    RETURN new;
END IF;

END;

This function is setted as trigger with "BEFORE INSERT". When null is returned, PostgreSQL don't insert the row as intended.

However, Entity Framework throws a System.Data.Entity.Infrastructure.DbUpdateException, with the expectable message A null store-generated value was returned for a non-nullable member 'table_id' ; table_id is obviously never setted because the row was rejected.

I wanted to know how can I tell Entity Framework to juste ignore the row instead of triggering an exception and continue the insert of the next rows.