Warning: Trying to access array offset on value of type bool error when upgrading to PHP 8.0

Question

When upgrading our website to PHP 8.0, we are faced with the following error:

Warning: Trying to access array offset on value of type bool

This relates to the following line of code:

$meta_value = $meta_values[ $meta_tuple['object_id'] ];

Code for the whole function is:

function wpsc_get_meta( $meta_key, $object_type, $object_id = 0 ) {

    global $wpdb;

    $cache_object_id = $object_id = (int) $object_id;
    $meta_key = wpsc_sanitize_meta_key( $meta_key );

    $meta_tuple = compact( 'object_type', 'object_id', 'meta_key' );
    $meta_tuple = apply_filters( 'wpsc_get_meta', $meta_tuple );

    // Get cached meta
    $meta_value = wp_cache_get( $cache_object_id, $meta_tuple['object_type'] );

    // If not cached, get and cache all object meta
    if ( $meta_value === false ) {
        $meta_values = wpsc_update_meta_cache( $meta_tuple['object_type'], $meta_tuple['object_id'] );
        $meta_value = $meta_values[ $meta_tuple['object_id'] ];
    }

    if ( isset( $meta_value[ $meta_tuple['meta_key'] ] ) ) {
        return maybe_unserialize( $meta_value[ $meta_tuple['meta_key'] ] );
    }

    return '';
}

Any suggestions how we could fix the above code for PHP 8.0 compatibility?

Rolled back to PHP 7.4, and the warning disappears.

Answer 1

You can change this

if ( isset( $meta_value[ $meta_tuple['meta_key'] ] ) ) {
    return maybe_unserialize($meta_value[$meta_tuple['meta_key']]);
}

to (see Null coalescing operator)

if ($meta_value[ $meta_tuple['meta_key']] ?? null)
   return maybe_unserialize($meta_value[$meta_tuple['meta_key']]);
}

or (old school)

if ( 
     is_array($meta_value)
     && isset( $meta_value[ $meta_tuple['meta_key'] ] ) 

) {
    return maybe_unserialize($meta_value[$meta_tuple['meta_key']]);
}