union_2d doesn't work

[albertsun]

Here's a test case, two boxes right next to each other.

$p([[0,0],[0,1],[1,1],[1,0]]).union_2d($p([[1,0],[1,1],[2,1],[2,0]]))

This returns null.

Those don't overlap, maybe that's the problem. But, this doesn't work either.

$p([[0,0],[0,1],[1,1],[1,0]]).union_2d($p([[0,0],[1,1],[2,1],[2,0]]))

This returns null too.