# Visit the entity `e`.
	#
	# This method setups `current_entity` and call `visit`.
	# If `e` is null, nothing is done.
	fun enter_visit(e: nullable MEntity) do
		if e == null then return
		if not accept_mentity(e) then return
		var old_entity = current_entity
		current_entity = e
		visit(e)
		current_entity = old_entity
	end