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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_check(self, check):
 """Add a check into the scheduler checks list :param check: check to add :type check: alignak.check.Check :return: None """

        if check is None:
            return
        if check.uuid in self.checks:
            logger.debug("Already existing check: %s", check)
            return
        logger.debug("Adding a check: %s", check)

        # Add a new check to the scheduler checks list
        self.checks[check.uuid] = check
        self.nb_checks += 1

        # Raise a brok to inform about a next check is to come ...
        # but only for items that are actively checked
        item = self.find_item_by_id(check.ref)
        if item.active_checks_enabled:
            self.add(item.get_next_schedule_brok())