Update changelog

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Fixed
+
+- Resolved an exception in the `GET api/v1/portfolio/holding/:dataSource/:symbol` endpoint for cash positions
+
 ## 3.31.0 - 2026-07-20
 
 ### Changed