modify_shared_link removing expiration date

Cross posting from http://stackoverflow.com/questions/34728081/modify-shared-link-settings-how-to-remove-expiration 

Basically, I don't see how I can use sharing/modify_shared_link to remove the expiration date from a link. This can be done from the Dropbox web UI, so I'd hope it is possible to do with the API. Any advice would be appreciated.

 

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I'm using v2 of the core API with HTTP directly, the method https://www.dropbox.com/developers/documentation/http/documentation#sharing-modify_shared_link_settings . I have no problems changing the visiblity, password and expiration date of a link, but I can't see how to *remove* the expiration entirely.

I've tried

• not sending 'expires' at all in my request while changing other properties - no effect
• setting 'expires' to the the JSON literal null - no effect
• setting 'expires' to a time in the past - gives a 'invalid_settings' error
• setting 'expires' to an empty string - gives a "time data " " does not match format '%Y-%m-%dT%H:%M:%SZ'" error.

I'm kind of at a loss here, is there something obvious I'm missing?