Document explicit null overrides pattern for deleting parameters

Add comprehensive documentation to parameter-names.mdx explaining how to use
explicit null values in overrides files to delete parameters from the base
OpenAPI specification.

Documentation includes:
- Clear explanation of when to use null overrides (duplicate identifiers,
  deprecated parameters, simplifying SDK interface)
- Warning about breaking changes when deleting parameters
- Example for deleting a single parameter using 'parameters: [null]'
- Example for deleting multiple parameters
- Real-world example from Vercel SDK showing how to resolve duplicate
  identifier errors between query parameters and request body properties

This pattern was successfully used to fix TypeScript compilation errors in
the Vercel SDK where slug query parameters conflicted with slug request
body properties.

Related PR: fern-demo/vercel-fern-config#13

Co-Authored-By: [email protected] <[email protected]>

Author: devin-ai-integration[bot]

fern/products/api-def/openapi-pages/extensions/parameter-names.mdx

@@ -63,3 +63,86 @@ paths:
             type: string
           required: false
 ```
+
+## Delete parameters with null overrides
+
+You can use explicit `null` values in your overrides file to delete parameters from the base specification. This is useful when:
+
+- Resolving duplicate identifier conflicts between query parameters and request body properties
+- Removing deprecated or unnecessary parameters from the SDK
+- Simplifying the SDK interface by hiding internal parameters
+
+<Warning>
+Deleting parameters is a breaking change. Parameters removed via null overrides will not be available in the generated SDK, even though they exist in the base OpenAPI specification.
+</Warning>
+
+### Delete a single parameter
+
+To delete the first parameter from an endpoint, use `parameters: [null]` in your overrides file:
+
+```yaml title="overrides.yml" {5-6}
+paths:
+  "/edge-config":
+    post:
+      x-fern-sdk-group-name: edgeConfig
+      x-fern-sdk-method-name: create
+      parameters:
+        - null
+```
+
+This removes the first parameter defined in the base specification for this endpoint.
+
+### Delete multiple parameters
+
+To delete multiple parameters, add multiple `null` entries:
+
+```yaml title="overrides.yml" {5-8}
+paths:
+  "/users":
+    get:
+      x-fern-sdk-group-name: users
+      x-fern-sdk-method-name: list
+      parameters:
+        - null  # Deletes first parameter
+        - null  # Deletes second parameter
+```
+
+### Real-world example: Resolving duplicate identifiers
+
+A common use case is resolving duplicate identifier errors when a query parameter and request body property have the same name. In this example, both the query parameter `slug` and the request body property `slug` would cause a TypeScript compilation error:
+
+<CodeGroup>
+```yaml title="openapi.yml"
+paths:
+  "/edge-config":
+    post:
+      operationId: create_edge_config
+      parameters:
+        - name: slug
+          in: query
+          description: "The Team slug"
+          schema:
+            type: string
+      requestBody:
+        content:
+          application/json:
+            schema:
+              type: object
+              properties:
+                slug:
+                  type: string
+                  description: "The Edge Config slug"
+```
+
+```yaml title="overrides.yml"
+paths:
+  "/edge-config":
+    post:
+      x-fern-sdk-group-name: edgeConfig
+      x-fern-sdk-method-name: create
+      parameters:
+        - null  # Removes the query parameter slug
+```
+</CodeGroup>
+
+After applying the override, the generated SDK will only include the request body `slug` property, eliminating the duplicate identifier error.