No autoincrement for Integer Primary key in sqlite3

In the sqlite3 faq, it is mentioned that an integer primary key being fed a null value would autoincrement. But this is not happening for me.

to replicate, a table in sqlite3, CREATE TABLE dummy( serial_num INTEGER PRIMARY KEY, name TEXT); and fill it using python,

import sqlite3 as lite
con = lite.connect('some.db')
cur=con.cursor()
data = "someone's name"
cur.execute("INSERT INTO dummy VALUES(NULL, ?)", data)
con.commit()

The first attribute serial_num is being shown blank while the name attribute is fine. When I do SELECT serial_num FROM dummy I just get a bunch of blank spaces. What am I doing wrong?