changelog(): updated with entry for #2912 and #6287, closes #2912

CHANGELOG.md

@@ -18,6 +18,7 @@
 * **Background Tasks**: Now support automatic purging of old rendered images, closes [#2172](https://github.com/grafana/grafana/issues/2172)
 * **Dashboard**: After inactivity hide nav/row actions, fade to nice clean view, can be toggled with `d v`, also added kiosk mode, toggled via `d k` [#6476](https://github.com/grafana/grafana/issues/6476)
 * **Dashboard**: Improved dashboard row menu & add panel UX [#6442](https://github.com/grafana/grafana/issues/6442)
+* **Graph Panel**: Support for stacking null values [#2912](https://github.com/grafana/grafana/issues/2912), [#6287](https://github.com/grafana/grafana/issues/6287), thanks @benrubson!
 
 ### Breaking changes
 * **SystemD**: Change systemd description, closes [#5971](https://github.com/grafana/grafana/pull/5971)