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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 export_kappa_cm(model, fname=None):
 """Return a networkx graph representing the model's Kappa contact map. Parameters model : pysb.core.Model A PySB model to be exported into a Kappa CM. fname : Optional[str] A file name, typically with .png or .pdf extension in which the CM is rendered using pygraphviz. Returns ------- npygraphviz.Agraph A graph object representing the contact map. """

    from .kappa_util import cm_json_to_graph
    kappa = _prepare_kappa(model)
    cmap = kappa.analyses_contact_map()
    cm = cm_json_to_graph(cmap)
    if fname:
        cm.draw(fname, prog='dot')
    return cm