> 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.

## 2.19.5

**`(fix):`** Fix missing client-level headers for endpoints without endpoint-specific headers.

Previously, endpoints that didn't have endpoint-specific headers (like custom request headers)
would not include client-level headers (API key, SDK version, additional headers) in their
HTTP requests. This caused authentication failures for APIs that rely on headers set at the
client level.

The fix ensures that all endpoints now properly merge headers from:

* Client options headers (API key, SDK version, etc.)
* Client additional headers (user-provided at client construction)
* Request options additional headers (user-provided per-request)

## 2.19.4

**`(fix):`** Fix missing `[Optional]` and/or `Nullable` attributes on generated properties with defaults.

## 2.19.3

**`(fix):`** Fully unwrap optional-nullable wrappers when generating undiscriminated unions.

## 2.19.2

**`(fix):`** Fixes missing references to Core utilities in interface files for the Optional wrapper.

## 2.19.1

**`(fix):`** Fix nullable element types in collections to correctly preserve nullable markers.

Previously, nullable types nested inside collections would incorrectly strip the inner nullable marker:

* `nullable<list<nullable<string>>>` incorrectly generated `IEnumerable<string>?`
* `nullable<map<string, nullable<Address>>>` incorrectly generated `Dictionary<string, Address>?`

Now generates correctly:

* `nullable<list<nullable<string>>>` generates `IEnumerable<string?>?`
* `nullable<map<string, nullable<Address>>>` generates `Dictionary<string, Address?>?`
* `optional<map<string, nullable<string>>>` generates `Dictionary<string, string?>?`