#1: "GetObject failed..." error when applying mapping with error, should warn with proper messaging (ex: "...'Hips' not found").
#2: Configure button disapears when error is thrown with Optimize Game Objects enabled.

repro:
-open project
-select UChar
-importer, Rig, Configure...
-remove "joint_Pelvis" from Hips mapping
-Apply...
bug#1: un-expected error in the console...
GetObject failed to find Object for Library Representation
UnityEditor.DockArea:OnGUI()

-Click Done
bug#2: Configure button is no longer visible. It should still be there.
workaround: Un-apply (disable) "Optimize Game Objects"... Configure button re-appears.

If OGO is not enabled, this bug is not repro.