BoxSDK iOS: modified_at field value is empty in listItems API call

I am using BoxSDK for iOS 4.3.0 to list folder items using files.listItems API call. I have added the fields listed below as parameter to this method but "content_modified_at", "content_created_at", "created_at", "modified_at" are nil in the resulting File and Folder objects. However I can see in the SDK debug log that body of the response is returning valid values, but SDK is not extracting them into classes. Could you please look if that's the case? I can see the values for all other fields requested, except for dates.

["id", "type", "is_externally_owned", "name", "owned_by", "content_modified_at", "content_created_at", "created_at", "modified_at"]