code: def get_next_node(self, process_name):
          
          if process_name not in self.process_hierarchy:
              raise ValueError('unable to compute the next_node due to unknown process: {0}'.format(process_name))
  
          time_qualifier = self.process_hierarchy[process_name].process_entry.time_qualifier
          return self._get_next_node(time_qualifier)
docs: :return: <AbstractTreeNode> next node to process by a process with process_name