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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 update_nexusport_binding(port_id, new_vlan_id):
 """Updates nexusport binding."""

    if not new_vlan_id:
        LOG.warning("update_nexusport_binding called with no vlan")
        return
    LOG.debug("update_nexusport_binding called")
    session = bc.get_writer_session()
    binding = _lookup_one_nexus_binding(session=session, port_id=port_id)
    binding.vlan_id = new_vlan_id
    session.merge(binding)
    session.flush()
    return binding