Trigger not being called, why? - sql

Question

So I have the following function that the trigger calls when I insert rows into a table called 'auxi'. It seems not to work since I have the value 'id_usuario' with NULL on my table and the trigger is supposed to avoid that.
CREATE OR REPLACE FUNCTION firstRestriction() RETURNS Trigger
AS $$
DECLARE
operation boolean = false;
BEGIN
RAISE NOTICE 'HERE %',operation;
operation = operation OR isNULL(new.periodo, 'periodo');
operation = operation OR isNULL(new.id_usuario, 'id_usuario');
operation = operation OR isNULL(new.fecha_hora_retiro, 'fecha_hora_retiro');
operation = operation OR isNULL(new.origen_estacion, 'origen_estacion');
operation = operation OR isNULL(new.destino_estacion, 'destino_estacion');
operation = operation OR isNULL(new.tiempo_uso, 'tiempo_uso');
/*operation = operation OR isLessThanZero(new.tiempo_uso, 'tiempo_uso');*/
IF operation THEN
raise notice 'No se pudo insertar % % % % % %',new.periodo, new.id_usuario, new.fecha_hora_retiro,new.origen_estacion
,new.destino_estacion, new.tiempo_uso;
return NULL;
ELSE
return new;
END IF;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER checkFirstRestriction
BEFORE INSERT ON auxi
FOR EACH ROW
EXECUTE PROCEDURE firstRestriction();
And then I do
CREATE OR REPLACE FUNCTION cond1()
RETURNS VOID AS $$
BEGIN
INSERT INTO auxi
SELECT *
FROM datos_recorrido;
END;
$$ LANGUAGE PLPGSQL;
Also isNull is the following function
CREATE OR REPLACE FUNCTION isNULL(field anyelement, information TEXT) RETURNS boolean
AS $$
BEGIN
IF field IS NULL THEN
raise notice 'El campo % es NULL', information;
return true;
ELSE
return false;
END IF;
END;
$$ LANGUAGE plpgsql;
And then at certain point I call my funciton cond1().
I think my trigger is never being called. Could that be possible?