FB.Feed() "properties" argument not working as expected

According to facebook for unity documentation, Facebook.feed has an argument named properties that will append additional links to a facebook post (see https://developers.facebook.com/docs/unity/reference/current/FB.Feed).

This works:

     FB.Feed(
         link : linkString, 
         linkName : linkNameString, 
         linkCaption : thisFeedItem.details, 
         linkDescription : thisFeedItem.title, 
         picture : FBPicLink(), 
         callback : ShareDone
         //properties: shareLinks
     );

This doesn't:

     FB.Feed(
         link : linkString, 
         linkName : linkNameString, 
         linkCaption : thisFeedItem.details, 
         linkDescription : thisFeedItem.title, 
         picture : FBPicLink(), 
         callback : ShareDone,
         properties: shareLinks
     );

The error I get is precompile: "No overloaded method for FB.Feed takes 7 arguments."