update changelog

CHANGELOG.md

@@ -16,6 +16,7 @@ This changelog documents the changes between release versions.
 
 - Upgrade dependencies to get fix for RUSTSEC-2024-0421, a vulnerability in domain name comparisons ([#138](https://github.com/hasura/ndc-mongodb/pull/138))
 - Aggregations on empty document sets now produce `null` instead of failing with an error ([#136](https://github.com/hasura/ndc-mongodb/pull/136))
+- Handle collection validators with object fields that do not list properties ([#140](https://github.com/hasura/ndc-mongodb/pull/140))
 
 #### Fix for RUSTSEC-2024-0421 / CVE-2024-12224
 
@@ -31,6 +32,25 @@ it uses the affected library exclusively to connect to MongoDB databases, and
 database URLs are supplied by trusted administrators. But better to be safe than
 sorry.
 
+#### Validators with object fields that do not list properties
+
+If a collection validator species an property of type `object`, but does not specify a list of nested properties for that object then we will infer the `ExtendedJSON` type for that property. For a collection created with this set of options would have the type `ExtendedJSON` for its `reactions` field:
+
+```json
+{
+  "validator": {
+    "$jsonSchema": {
+      "bsonType": "object",
+      "properties": {
+        "reactions": { "bsonType": "object" },
+      }
+    }
+  }
+}
+```
+
+If the validator specifies a map of nested properties, but that map is empty, then we interpret that as an empty object type.
+
 ## [1.5.0] - 2024-12-05
 
 ### Added