Update CHANGELOG.md

CHANGELOG.md

@@ -3,6 +3,7 @@
 * `convert`: When running in "unsafe mode" (which allows additional conversions that can potentially fail with certain input values), we'll now allow converting from a map type to an object type with optional attributes as long as all of the _present_ map elements are compatible with their corresponding optional attributes.
 
     It's still a dynamic error to convert a map whose element type is incompatible with any of the attributes that _do_ have corresponding keys in the given map. ([#139](https://github.com/zclconf/go-cty/pull/139))
+* `convert`: Will now produce correct type constraints when the input value is null and the target type has optional attributes. In this case the conversion process must remove the optional attribute annotations because those are only for type conversion purposes and have no meaning when used in the type constraint for a null or unknown value. ([#140](https://github.com/zclconf/go-cty/pull/140))
 
 # 1.11.1 (October 17, 2022)