Box Shared Link for Files through Salesforce Apex Class

Hi, I have been scouring your site and the Internet looking for how to create a shared link using the Box.com Salesforce SDK. I have tried the solution found here: https://community.box.com/t5/Platform-and-Development-Forum/Box-Shared-Link-through-Salesforce-Apex-Class/td-p/50822 but the CreateSharedLink() function seems to be different for Files than it is for Folders.  no matter what I try it will not create a link if one did not previously exist. Whenever I try SharedLink in the Response is "null".  to be clear this is on files the api previously uploaded. 

according to the debug logs, my request body currently looks like

{"access":"open","permissions":{"can_preview":true,"can_download":true},"can_download":true}

but this has changed as I've tried 

on a related note: is line 102 of this file supposed to be password? it seems odd given line 101 and line93. https://github.com/box/box-salesforce-sdk/blob/master/src/classes/BoxSharedLink.cls

Thank you for your time!