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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_job_control_plane(self):
 """ Add a JobControlPlane operator to the topology, if one has not already been added. If a JobControlPlane operator has already been added, this has no effect. """

        if not self._has_jcp:
            jcp = self.graph.addOperator(kind="spl.control::JobControlPlane", name="JobControlPlane")
            jcp.viewable = False
            self._has_jcp = True