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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 refresh_fqdn_cache(force=False):
    '''
    Force refreshes all FQDNs used in rules.

    force
        Forces all fqdn refresh

    CLI Example:

    .. code-block:: bash

        salt '*' panos.refresh_fqdn_cache
        salt '*' panos.refresh_fqdn_cache force=True

    '''
    if not isinstance(force, bool):
        raise CommandExecutionError("Force option must be boolean.")

    if force:
        query = {'type': 'op',
                 'cmd': '<request><system><fqdn><refresh><force>yes</force></refresh></fqdn></system></request>'}
    else:
        query = {'type': 'op', 'cmd': '<request><system><fqdn><refresh></refresh></fqdn></system></request>'}

    return __proxy__['panos.call'](query)