Problems with Xbox logins when people have unticked "display on public profile"

I am using GetBungieNetUser to get the username that can then be used with SearchDestinyPlayer to get the membershipId so I can get the account summary. There is no problem with PSN users. From the JSON you get with GetBungieNetUser I grab Response.psnId. This is always there. However things are not so simple on Xbox. With most users I can grab 'Response.user.xboxDisplayName'. However if on Bungie.net users in linked accounts have unticked "display on public profile" then 'Response.user.xboxDisplayName' is not in the JSON. By the way nothing changes in the PSN JSON when you change this tick! So I now I have to grab 'Response.user.displayName'. This works for some users. However I think people who have a different Xbox display name to the one which displays in Destiny result in a failed attempt to get the membershipId. Help!