SQL & PL/SQL

Why i'm getting error "ORA-06502: PL/SQL: numeric or value error" in below code.

create table bc (
  a number, 
  b varchar2(10)
);


declare
  type t_bc_a is table of bc.a%type;
  type t_bc_b is table of bc.b%type;
  l_bc_a t_bc_a;
  l_bc_b t_bc_b;
begin
  dbms_output.put_line('1');
  select a, b bulk collect into l_bc_a, l_bc_b from bc;
   dbms_output.put_line('2');
   if l_bc_a is null then
     dbms_output.put_line('2.1'); 
   else
     dbms_output.put_line('2.2, l_bc_a.count=' || l_bc_a.count); 
     
   end if;
  for i in l_bc_a.first .. l_bc_a.last loop
   dbms_output.put_line('3');
    dbms_output.put_line(l_bc_a(i) || ', ' || l_bc_b(i));
  end loop;
end;

/*
1
2
2.2, l_bc_a.count=0
ORA-06502: PL/SQL: numeric or value error
*/

Table "bc" is empty, and i expect for-loop to never do any cycle/step, but i get error. Why the error is there.