IsDate function in plpgsql

["Sistemas C.M.P." <sistemascmp(at)redynet4(dot)com(dot)ar>]

A few days ago, someone in this list gives  me a function (plpgsql) that evaluates if a string is a valid date or not.

It returns 1 or 0 (valid/Not Valid)

The problem is that if the argument is a NULL field the function returns 1.

I don't have experience with plpgsql language.

This is the function

 

begin
  perform $1::date;
  return 1;
exception when others then
  return 0;

end