update changelogs

Author: tstanmay13

fern/products/sdks/overview/java/changelog/2025-09-30.mdx

@@ -1,3 +1,8 @@
+## 3.8.4
+**`(fix):`** Fixed code generation for undiscriminated unions with optional types. Generated code now correctly
+wraps optional values with `Optional.of()`, and wire tests are properly generated by default.
+
+
 ## 3.8.1
 **`(fix):`** Append decimal to whole number double literals to prevent compilation errors.