Update CHANGELOG.md

CHANGELOG.md

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 # HCL Changelog
 
-## v2.15.1 (Unreleased)
+## v2.16.0 (Unreleased)
+
+### Bugs Fixed
+
+* ext/typeexpr: Modify the `Defaults` functionality to implement additional flexibility. HCL will now upcast lists and sets into tuples, and maps into objects, when applying default values if the applied defaults cause the elements within a target collection to have differing types. Previously, this would have resulted in a panic, now HCL will return a modified overall type. ([#574](https://github.com/hashicorp/hcl/pull/574))
+
+### Enhancements
+
+* ext/typeexpr: Users should return to the advice provided by v2.14.0, and apply the go-cty convert functionality *after* setting defaults on a given `cty.Value`, rather than before. ([#574](https://github.com/hashicorp/hcl/pull/574))
 
 ## v2.15.0 (November 10, 2022)