docs: add collapse-optional-nullable flag to Java SDK configuration (#1882)

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: [email protected] <[email protected]>

Author: devin-ai-integration[bot]

fern/products/sdks/overview/java/configuration.mdx

@@ -27,6 +27,10 @@ Specifies the name of the base exception class that all generated exceptions wil
 The provided string will be used as the client class name.
 </ParamField>
 
+<ParamField path="collapse-optional-nullable" type="boolean" default="false" required={false} toc={true}>
+When enabled, generates `OptionalNullable<T>` types for merge patch request fields to distinguish between three states: absent (field not provided), null (field explicitly set to null), and present (field has a non-null value). This enables proper handling of JSON Merge Patch semantics where omitting a field, setting it to null, and providing a value have different meanings.
+</ParamField>
+
 <ParamField path="custom-dependencies" type="List<string>" required={false} toc={true}>
 
 <Markdown src="/snippets/pro-plan.mdx"/>
@@ -140,4 +144,4 @@ Provides a description of the SDK package that will appear in package metadata a
 </ParamField>
 <ParamField path="reference-url" type="string" required={false} toc={true}>
 Sets the reference URL (typically the API documentation or project website) that will be included in the package metadata for users to find additional information.
-</ParamField>
+</ParamField>