In Radar as <rdar://problem/8712674>
There are some reports from the field of an exception thrown in [WebAuthenticationPanel setUpForChallenge] where a nil string is being passed to [NSCell setStringValue:].
There are several calls to setStringValue: in that method, but it appears that only the call that passes "realm" could be the culprit.
Created attachment 75386 [details]
Patch to substitute an empty string for a nil string (for realm)
Fixed in r73143.