Error message: Uncaught Error: Unsupported operand types

WordPress version 5.4.2
Current plugin: Related Posts Lite (version 1.12)
PHP version 7.2.31

Error Details
=============
An error of type E_ERROR was caused in line 108 of the file /home/xxx/blog/wp-content/plugins/related-posts-lite/backend/metaboxes/default-content.php. Error message: Uncaught Error: Unsupported operand types in /home/xxx/blog/wp-content/plugins/related-posts-lite/backend/metaboxes/default-content.php:108
Stack trace:
#0 /home/xxx/blog/wp-includes/class-wp-hook.php(289): RPLDefaultContent->save(3868)
#1 /home/xxx/blog/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(NULL, Array)
#2 /home/xxx/blog/wp-includes/plugin.php(478): WP_Hook->do_action(Array)
#3 /home/xxx/blog/wp-includes/post.php(4153): do_action(‘save_post’, 3868, Object(WP_Post), true)
#4 /home/xxx/blog/wp-includes/post.php(4244): wp_insert_post(Array, false)
#5 /home/xxx/blog/wp-admin/includes/post.php(409): wp_update_post(Array)
#6 /home/xxx/blog/wp-admin/post.php(227): edit_post()
#7 {main}
thrown

Replace the old code:
$rpl_data += $params; ====> $rpl_data = array_merge($rpl_data, $params);