Update changelog

Author: T4rk1n

CHANGELOG.md

@@ -2,6 +2,12 @@
 All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](https://semver.org/).
 
+## UNRELEASED
+
+## Fixed
+
+- [#2854](https://github.com/plotly/dash/pull/2854) Fix dcc.Dropdown resetting empty values to null and triggering callbacks. Fixes [#2850](https://github.com/plotly/dash/issues/2850)
+
 ## [2.17.0] - 2024-05-03
 
 ## Added