WordPRress database error

Hi,

I get this error:

[15-Apr-2020 16:10:59 UTC] WordPress database error Got error ’empty (sub)expression’ from regexp for query SELECT MAX(CAST(SUBSTRING(meta_value,1,4) AS UNSIGNED)) as new_number FROM wp_postmeta WHERE meta_key = ‘_wcson_order_number’ AND meta_value REGEXP SUBSTRING(‘5444’,1,0) made by require(‘wp-blog-header.php’), require_once(‘wp-includes/template-loader.php’), do_action(‘template_redirect’), WP_Hook->do_action, WP_Hook->apply_filters, WC_AJAX::do_wc_ajax, do_action(‘wc_ajax_checkout’), WP_Hook->do_action, WP_Hook->apply_filters, WC_AJAX::checkout, WC_Checkout->process_checkout, WC_Checkout->create_order, do_action(‘woocommerce_checkout_update_order_meta’), WP_Hook->do_action, WP_Hook->apply_filters, WCSON_ORDER_NUMBER::wcson_order_number, WCSON_ORDER_NUMBER::wcson_generate_new_order_number

This error is generated each time someone makes a purchase on my site.
It is caused by your plugin.
What could be the solution?

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