[luantaraschi]

Follow up to #16457, which covered the flat case. The nested branch of Schema#remove() has the same two problems, and one of them throws:

const schema = new Schema({ n: { m: { type: Map, of: Number } } });
schema.remove('n');
// TypeError: Cannot convert undefined or null to object
//     at _deletePath (lib/schema.js:2806:17)

A map registers its values under <path>.$* in paths, so the nested branch walks ['n.m', 'n.m.$*'] and calls _deletePath on each. _deletePath walks schema.tree down the pieces, and by the time it gets to n.m.$* the parent tree.n.m has already been deleted by the previous iteration, so branch is undefined and the delete throws. $* has no branch of its own in the tree in any case.

So _deletePath now stops when a piece along the way is missing. Nothing to delete is not an error there.

With that out of the way the second problem shows: the nested branch never filtered mapPaths, which is what the flat branch does. Measured after schema.remove('n'), before and after:

	paths	mapPaths	pathType('n.m')
before	['_id']	['n.m.$*']	real
after	['_id']	[]	adhocOrUndefined

So the schema kept answering for a path it had just removed, which is the same thing #16457 described, only reached through a nested parent. Both branches now do the same cleanup.

Test in the remove() block. It fails on master on the first assertion, since remove throws before the rest runs.

test/schema.test.js passes 225. Full npm test here matches master, the only failure being an eachAsync timeout that reproduces on a clean checkout on this machine. eslint is clean.

[vkarpov15]

Thanks 👍