date_in function

I want to change the date from a field in a tuple in a trigger_function

create table example (   my_date datetime   ...
);

int na;
char select[20];

na = SPI_fnumber(trigdata->tg_relation->rd_att, "my_date");
memset(select, 0, sizeof(select));
sprintf(select, "1/1/2002");
newval = DirectFunctionCall1(date_in, CStringGetDatum(select));
rettuple = SPI_modifytuple(trigdata->tg_relation, rettuple, 1, &na, &newval, 
NULL);
if(rettuple == NULL) elog(ERROR, "my_function: %d returned by 
SPI_modifytuple", SPI_result);

when i test that my server goes down. What I missed ?