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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_networks(network_id=None):
 """Returns list of all networks that may be relevant on CVX"""

    session = db.get_reader_session()
    with session.begin():
        model = models_v2.Network
        networks = session.query(model).filter(model.project_id != '')
        if network_id:
            networks = networks.filter(model.id == network_id)
    return networks.all()