code: def push_identity(self, identifiers):
          
          if (not identifiers):
              msg = ("Specified Subject identifiers cannot be None or empty "
                     "for 'run as' functionality.")
              raise ValueError(msg)
  
          stack = self.get_run_as_identifiers_stack()
  
          if (not stack):
              stack = []
  
          stack.append(identifiers)
          session = self.get_session()
          session.set_internal_attribute(self.run_as_identifiers_session_key, stack)
docs: :type identifiers: subject_abcs.IdentifierCollection