Maybe schemars changed behavior to implicit defaults.
--- a/tests/schemars_0_8/snapshots/one_or_many_nested.json
+++ b/tests/schemars_0_8/snapshots/one_or_many_nested.json
@@ -6,3 +6,2 @@
     "optional_many": {
-      "default": null,
       "anyOf": [
