fix return type

Author: Suganth Sadaiyappan

nisystemlink/clients/assetmanagement/_asset_management_client.py

@@ -126,15 +126,16 @@ def delete_assets(self, ids: List[str]) -> models.DeleteAssetsResponse:
     @post("assets/{assetId}/file", args=[Path("assetId"), Field("fileIds")])
     def link_files(
         self, asset_id: str, file_ids: List[str]
-    ) -> models.LinkFilesPartialSuccessResponse:
+    ) -> Optional[models.LinkFilesPartialSuccessResponse]:
         """Link files to an asset.
 
         Args:
             asset_id: The ID of the asset to which files should be linked.
             file_ids: The list of file IDs to link.
 
         Returns:
-            LinkFilesPartialSuccessResponse: Response containing the results of the link operation.
+            Optional[LinkFilesPartialSuccessResponse]: None if all link files succeed, otherwise a response
+            containing the IDs of files that were successfully linked and those that failed.
 
         Raises:
             ApiException: If unable to communicate with the asset management service or if there are invalid arguments.