Warning: in_array() expects parameter 2 to be array, null given in

Hello,
i have noticed that i have a problem with a site. Under every page it shows a warning:
Warning: in_array() expects parameter 2 to be array, null given in /home/users/akselp01/public_html/domains/dent-guard.pl/public_html/wp-content/themes/oceanwp/functions.php on line 972

In functions it is:

}
function my_custom_available_payment_gateways( $gateways ) {
	$chosen_shipping_rates = ( isset( WC()->session ) ) ? WC()->session->get( 'chosen_shipping_methods' ) : array();

		if ( in_array( 'flat_rate:1', $chosen_shipping_rates ) ) :
		unset( $gateways['cod'] );
		
		elseif ( in_array( 'flat_rate:2', $chosen_shipping_rates ) ) :
		unset( $gateways['bacs'] );
		
		elseif ( in_array( 'flat_rate:3', $chosen_shipping_rates ) ) :
		unset( $gateways['cod'] );
		
		elseif ( in_array( 'flat_rate:4', $chosen_shipping_rates ) ) :
		unset( $gateways['bacs'] );

	endif;
	return $gateways;
}

What i can do to fix it?

Thanks!

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