^^&&^^

Edit File: class-upgrade-v1_7-settings.php

<?php
/**
 * Upgrade Settings class for batch
 *
 * @package   PUM
 * @copyright Copyright (c) 2023, Code Atlantic LLC
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Implements a batch processor for migrating existing popups to new data structure.
 *
 * @since 1.7.0
 *
 * @see PUM_Abstract_Upgrade_Popups
 */
class PUM_Upgrade_v1_7_Settings extends PUM_Abstract_Upgrade_Settings {

/**
	 * Batch process ID.
	 *
	 * @var    string
	 */
	public $batch_id = 'core-v1_7-settings';

/**
	 * Process needed upgrades on each popup.
	 *
	 * @param array $settings Current global popup maker settings.
	 */
	public function process_settings( $settings = [] ) {
		$changed = false;

// popmake_settings['newsletter_default_provider'] == '' should be changed to 'none'
		if ( isset( $settings['newsletter_default_provider'] ) && '' === $settings['newsletter_default_provider'] ) {
			$settings['newsletter_default_provider'] = 'none';
			$changed                                 = true;
		}

/**
		 * Save only if something changed.
		 */
		if ( $changed ) {
			PUM_Utils_Options::update_all( $settings );
		}
	}

}