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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 get_current_scene_node():
 """Return the name of the jb_sceneNode, that describes the current scene or None if there is no scene node. :returns: the full name of the node or none, if there is no scene node :rtype: str | None :raises: None """

    c = cmds.namespaceInfo(':', listOnlyDependencyNodes=True, absoluteName=True, dagPath=True)
    l = cmds.ls(c, type='jb_sceneNode', absoluteName=True)
    if not l:
        return
    else:
        for n in sorted(l):
            if not cmds.listConnections("%s.reftrack" % n, d=False):
                return n