The unit tests expect -1 (or a very large number) but SQLite is returning null instead.

Not sure why, -1 and null are both widely used sentinels, so maybe the test needs to look for both, or the values need harmonised at some point before it gets to this stage, or maybe it's just a bug somewhere.

relevant test is test_add_field in line 639 of lib/ddl/tests/ddl_test.php