Mention IdString#equals implementation change in 2.15 release notes
Change-Id: I8caa9fdc92b4c05b66f505e3bc4296f256e472db
diff --git a/releases/2.15.md b/releases/2.15.md
index 7ddf88c..2a50d4c 100644
--- a/releases/2.15.md
+++ b/releases/2.15.md
@@ -38,6 +38,14 @@
Changes can be switched between "work in progress" and "ready to review".
+### API
+
+* Instances of [IdString](https://gerrit.googlesource.com/gerrit/+/stable-2.15/gerrit-extension-api/src/main/java/com/google/gerrit/extensions/restapi/IdString.java)
+ used to return true when `equals` was given a String instance equal to the
+ IdString's URL-encoded value. This violates
+ [symmetry](https://en.wikipedia.org/wiki/Equivalence_relation#Definition), so
+ this behavior was removed: IdStrings now never compare equal to Strings.
+
### REST API
#### Changes
