get_obj (Weak::Key)

    # File lib/Borges/Utilities/WeakIdentityKeyHash.rb, line 120
        def get_obj
          unless ID_REV_MAP[self.object_id] == @internal_id then
            raise RefError, "Illegal Reference - probably recycled", caller(2)
          end

          begin
            return ObjectSpace._id2ref(@internal_id)
          rescue RangeError
            raise RefError, "Illegal Reference - probably recycled", caller(2)
          end
        end