> This page is for SDKs, version Legacy.
> For other versions, use one of these documentation indexes:
> - Current (default): https://buildwithfern.com/learn/sdks/current/llms.txt
> - Legacy: https://buildwithfern.com/learn/sdks/legacy/llms.txt

> For clean Markdown content of this page, append .md to this URL. For the complete documentation index, see https://buildwithfern.com/learn/llms.txt.

## 1.57.13

**`(fix):`** Calling a `SetXxx` setter on a value copy of a request or model type no longer
changes the JSON of the value it was copied from. The private `explicitFields`
bitmask is reached through a pointer, so a plain struct assignment aliased it and
`require` mutated it in place, making every explicit-field bit set on one copy
visible in all of them (e.g. `copied.SetOptions(...)` added `"options":null` to
the original's body). The bitmask is now replaced rather than mutated, so each
copy gets its own on first write.