update changelogs

Author: tstanmay13

fern/products/sdks/overview/java/changelog/2025-08-25.mdx

@@ -0,0 +1,11 @@
+## 2.42.0
+**`(feat):`** Add support for semantic distinction between `nullable<T>` and `optional<T>` types via `use-nullable-annotation` flag.
+When enabled, `nullable<T>` generates as raw type `T` with `@Nullable` annotation, while `optional<T>` remains as `Optional<T>`.
+This provides proper API semantics for fields that can be null vs those that may be absent from requests.
+
+```yaml
+customConfig:
+  use-nullable-annotation: true
+```
+
+