Mongoose's findById method casts the id parameter to the type of the model's _id field so that it can properly query for the matching doc. This is an ObjectId but "foo" is not a valid ObjectId so the cast fails.
This doesn't happen with 41224d776a326fb40f000001 because that string is a valid ObjectId.
One way to resolve this is to add a check prior to your findById call to see if id is a valid ObjectId or not like so:
if (id.match(/^[0-9a-fA-F]{24}$/)) { // Yes, it's a valid ObjectId, proceed with `findById` call. }

Mongoose's `findById` method casts the `id` parameter to the type of the model's `_id` field so that it can properly query for the matching doc. This is an ObjectId but `"foo"` is not a valid ObjectId so the cast fails.
This doesn't happen with `41224d776a326fb40f000001` because that string is a valid ObjectId.
One way to resolve this is to add a check prior to your `findById` call to see if `id` is a valid ObjectId or not like so:
<!-- language: lang-js -->
if (id.match(/^[0-9a-fA-F]{24}$/)) { // Yes, it's a valid ObjectId, proceed with `findById` call. }