array_key_exists(): Argument #2 ($array) must be of type array, WP_Term given

PHP8 with installed plugin Fusion Page Builder and when trying to create new page (the URL is example.com/wp-admin/post-new.php) you are getting the following error:

TypeError thrown

array_key_exists(): Argument #2 ($array) must be of type array, WP_Term given

Issue lies with the php function array_key_exists which is deprecated from PHP version 8 if the second parameter is an object. It works only on arrays.

To get around this, edit the problem lies in the file wp-content/plugins/fusion-builder/inc/helpers.php.

The lines 239-243:

if ( array_key_exists( 'slug', $cat ) && array_key_exists( 'name', $cat ) ) {
    $label = $cat->name . ( ( array_key_exists( 'count', $cat ) ) ? ' (' . $cat->count . ')' : '' );
    $post_categories[ urldecode( $cat->slug ) ] = $label;
    }
}

Replace with:

/** @var WP_Term $cat */
foreach ( $get_categories as $cat ) {
    if ( property_exists( $cat, 'slug' ) && property_exists( $cat, 'name' ) ) {
    $label = $cat->name . ( ( property_exists( $cat, 'count') ) ? ' (' . $cat->count . ')' : '' );
    $post_categories[ urldecode( $cat->slug ) ] = $label;
    }
}

Also the line 278-283:

if ( $get_terms && is_array( $get_terms ) ) {
    foreach ( $get_terms as $term ) {
        $label = $term->name . ( ( array_key_exists( 'count', $term ) ) ? ' (' . $term->count . ')' : '' );
        $post_tags[ urldecode( $term->slug ) ] = $label;
    }
}

Replace with the:

if ( $get_terms && is_array( $get_terms ) ) {
    foreach ( $get_terms as $term ) {
        /** @var WP_Term $term */
        $label = $term->name . ( ( property_exists( $term, 'count' ) ) ? ' (' . $term->count . ')' : '' );
        $post_tags[ urldecode( $term->slug ) ] = $label;
    }
}

Maybe the person that created this plugin can issue the new version because there are a lot of broken WordPress installations around the Internet.

Thanks, Petar.