Missing numerical value

CREATE TABLE qa (
    question TEXT,
    answer INTEGER
);

INSERT INTO qa (question, answer) VALUES ('2+2', 4);
INSERT INTO qa (question, answer) VALUES ('2-2', 0);

INSERT INTO qa (question) VALUES ('Meaning of life?');

SELECT * from qa;

$ sqlite3 < examples/missing-integer-value.sql
2+2|4
2-2|0
Meaning of life?|

╭──────────────────┬────────╮
│     question     │ answer │
╞══════════════════╪════════╡
│ 2+2              │      4 │
│ 2-2              │      0 │
│ Meaning of life? │ NULL   │
╰──────────────────┴────────╯