wordpress function breaks wp-admin

PHP Snippet 1:

function geo_client_currency( $client_currency ) {
    if ( WC()->customer ) {
        $country = WC()->customer->get_shipping_country();

        /**
         * Assuming more are going to be added otherwise a switch is overkill.
         * Short example: $client_currency = ( 'GB' === $country ) ? 'GBP' : 'EUR';
         */
        switch ( $country ) {
            case 'GB': 
                $client_currency = 'GBP'; 
                break;

            default: 
                $client_currency = 'EUR';
        }
    }

    return $client_currency;
}
add_filter( 'wcml_client_currency', 'geo_client_currency' );