SQL> create table test543
  2  (i varchar2(10));

Table created.
SQL> insert into test543  values(' ');

1 row created.

SQL> ed
Wrote file afiedt.buf

  1* insert into test543  values('        ')
SQL> /

1 row created.

SQL> ed
Wrote file afiedt.buf

  1* insert into test543  values(null)
SQL> /

1 row created.

SQL> commit;

Commit complete.

SQL> select i,length(i) from test543;

I           LENGTH(I)
---------- ----------
                    1
                           3

3 rows selected.